ELI5中文

Explained so anyone gets it

82 explainers · 8 series · 40 videos
Video
Latest · No. 82

What Do Dogs Learn by Sniffing Pee?

Every puddle is a signed letter: sniffing is reading, and peeing on top is writing back. Here's what's inside.

No. 82Animals5 minOct 6, 2026

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How a Web Page Gets MadeNo. 1 What Is a Black Hole?No. 33 A Power Strip for Your AI (MCP)No. 44 Why the Whole World Posts CatsNo. 7 One Minute to Add, a Lifetime to KeepNo. 16 What is ELI5?No. 52

Series

How AI WorksModels, agents, AI companies and their headlines — explained with everyday things.14 pieces Inside Computers & the InternetWeb pages, addresses, code, tiny computers and tap cards — things you use daily but can't quite explain.20 pieces Nature & ScienceClouds, black holes, landslides, wood and kitchen chemistry — how the world actually works.9 pieces AnimalsCats, dogs, zoo and wild animals — what they sense and why they do what they do.6 pieces Brain & BodyTip-of-the-tongue moments, morning pee, smoking and drinking — why our brains and bodies do this.8 pieces Culture & PopHolidays, myths, superheroes, games and talks — where the things everyone talks about come from.7 pieces Money & BusinessWhere money flows, and why some people get ahead and others don't.6 pieces Thinking ClearlyReading people, excuses, learning, getting things done and explaining well — tidying up how we think.12 pieces

Everything

Video

What Do Dogs Learn by Sniffing Pee?

Every puddle is a signed letter: sniffing is reading, and peeing on top is writing back. Here's what's inside.

No. 82Animals5 min
Video

How does a microprocessor actually work?

Billions of tiny on/off switches follow a list, one line at a time: fetch, understand, do — billions of beats a second.

No. 81Inside Computers & the Internet4 min
Video

What Happens Inside You When You Yell

One second of shouting puts your whole body to work: a brain alarm, a rush of adrenaline, slamming vocal cords, even extra strength.

No. 80Brain & Body5 min
Video

How Do Scientists Measure Millions of Light-Years?

No one has been to Andromeda and no ruler reaches that far. Astronomers built a four-rung ladder that starts with your thumb.

No. 79Nature & Science6 min
Video

How schizophrenia changes what feels real

Your brain tags every feeling as 'me' or 'not me' and flags what matters. When those get scrambled, inner words sound like voices and ordinary things feel like signals.

No. 78Brain & Body6 min
Video

Why a shop-watching AI works like a funnel

The smartest AI comes last: say what you want first, then let each picture pass through cheap checks before expensive ones.

No. 77How AI Works5 min
Video

Do cats and dogs know how long you’ve been gone?

They can't read clocks, but body rhythms, routines and maybe scent tell them time has passed. They notice 30 minutes vs 2 hours, but not 2 vs 4.

No. 76Animals5 min
Video

Why do some animals eat meat and others eat plants?

Nobody wrote animals a menu. Scissor teeth or millstone teeth, and gut helpers or none, decide what they can eat, shaped over generations.

No. 75Animals7 min
Video

Which Animal Has the Smelliest Poop?

There's no official champion, but there is a pattern: the more meat an animal eats, the worse its poop usually smells. Then there are otters.

No. 74Animals6 min
Video

Are Zoo Animals Happy, or Not?

Most zoo animals outlive their wild cousins. But is a longer life a happier one? It depends on the animal and the zoo, plus three things to look for on your next visit.

No. 73Animals7 min
Video

Peed before bed, drank nothing: why pee in the morning?

That morning pee isn't water from nowhere. Your kidneys filter your blood all night, just slower, and the bladder fills up by morning.

No. 72Brain & Body5 min
Video

What Is E2E in Software Testing?

A robot walks the whole path like a real user and checks the result. What end-to-end testing is, and why teams use only a few.

No. 71Inside Computers & the Internet5 min
Video

What Are TED Talks?

TED isn't a person: it stands for Technology, Entertainment, Design. How a money-losing conference became a place where ideas spread, why every talk is 18 minutes at most, TEDx, and the most-watched talk.

No. 70Culture & Pop3 min
Video

What Is Minecraft, Really?

A box of bricks with no instructions: the whole world is blocks you dig and stack, generated as you walk from a number called a seed. Survival, creative, redstone computers, and why it's the best-selling game ever.

No. 69Culture & Pop4 min
Video

Sushiro: The Plates That Count the Distance

Why does sushi on a belt stay fresh? Every Sushiro plate carries a tiny chip that tracks how far it has travelled; after about 350 metres it comes off, and the same data tells the kitchen what to make.

No. 68Money & Business4 min
Video

Why a word gets stuck on the tip of your tongue

You know the word but can't say it: your brain found the meaning, but the path to its sound is overgrown.

No. 67Brain & Body5 minReader question
Video

Why Do We Skip Whole Words When Typing?

It isn't carelessness: your brain hands words to your fingers one at a time and races ahead, so one never arrives. Then it fills the gap when you reread. How to catch it.

No. 66Brain & Body4 min
Video

Why Do We Forget What We Were About to Say?

It isn't your brain breaking: the thought sits on a tiny mental sticky-note board that gets crowded in conversation, and a new topic turns the page. Plus three small tricks.

No. 65Brain & Body4 min
Video

Why Wood Might Be the Material to Use More

A cubic metre of wood holds about a tonne of CO2. Swap some cement and steel for wood and buildings store carbon instead of releasing it — if the trees are replanted.

No. 64Nature & Science4 min
Video

Why Some Backpacks Feel Lighter

Same laptop, new bag, and it feels lighter. The weight didn't change: a good pack keeps it close, puts it on your hips, spreads it out, and stops it swinging.

No. 63Nature & Science4 min
Video

What Is a Video Project?

The finished video is like a PDF; the project is the PowerPoint you can still edit. What's inside, what export does, why keep the project, and a common trap.

No. 62Inside Computers & the Internet4 min
Video

Why Are Ancient Cities Buried?

Cities get buried by layers piling up in place: rebuilding on ruins, volcanic ash, floods and sand. Will the ground reach space? No, Earth's surface works like a slow conveyor belt.

No. 61Nature & Science4 min
Video

What Is Meta's Muse?

Earlier AI answered questions; Muse gets things done: email, trips, forms, payments. How it works, what it costs, and what to think about first.

No. 60How AI Works4 min
Video

Short or Long Videos: Which Helps You Learn?

It's not the length, it's who presses pause. The 8-second myth, the 6-to-9-minute sweet spot, two kinds of short, and what scrolling does.

No. 59Thinking Clearly4 min
Video

Books, Short Videos, or AI: Which Helps You Learn?

Learning depends on how hard your brain works, not the source. A classic experiment, the strengths of each way, and why AI can help or hurt.

No. 58Thinking Clearly4 min
Video

What Are You Really Smoking?

Nicotine hooks you; the smoke harms you. Why a cigarette feels relaxing, whether one a day is OK, what quitting does, and why it's hard.

No. 57Brain & Body4 min
Video

What Does Drinking Really Do for Us?

The fun of drinking is real, but it's a loan. Is a little good for you, what a red face means, why quitting is hard, and how to stop safely.

No. 56Brain & Body6 min
Video

Owe Money in Several Places? Which to Pay First

Like a fire, a leak and a dead bulb at once: sort debts by what happens if you don't pay, pick snowball or avalanche, map 13 weeks ahead, and talk early.

No. 55Money & Business8 min
Video

Where AI model names come from

Claude, GPT, Gemini, Qwen: every model name is three pieces — whose it is, how big, which version. And each brand has a story.

No. 54How AI Works5 min
Video

Why Do So Many Dogs Follow You to the Bathroom?

Common, but not every dog does it. Three research-backed reasons, three vet explanations not yet studied, and when following can signal separation anxiety.

No. 53Animals5 minReader question
Video

What is ELI5?

ELI5 explained the ELI5 way: where the four letters came from, four rules, why keeping it simple tests whether you really get it, and two common misunderstandings

No. 52Thinking Clearly6 min
Video

How Many Kinds of Clouds Are There?

The ten cloud types, learned through five Latin roots and a three-story sky: why "alto" clouds aren't the highest and which one brings thunder and hail.

No. 51Nature & Science5 minReader question
Video

The Story of Vishnu

The Hindu protector god in a few minutes: the three major gods, ten avatars and the churning of the ocean of milk.

No. 50Culture & Pop6 minReader question
Video

What Is DC Comics?

The home of Superman and Batman: a company that started with a 10-cent comic book, and has been rivals with Marvel for decades.

No. 49Culture & Pop4 min
Video

What Is Marvel?

From a comic-book company to one giant connected movie story: Spider-Man, Iron Man, the Avengers, and where to start watching.

No. 48Culture & Pop4 min
Video

Where China's National Day Comes From

The Oct 1, 1949 ceremony: 300,000 people, the first flag, 54 cannons and 28 salvos; how Oct 1 became National Day; and why only 3 of the 7 days off are legal.

No. 47Culture & Pop4 min
Video

Who Is Tibo from Codex?

Why programmers wait for his posts: when OpenAI's head of product says "reset," everyone's AI usage allowance refills. Codex, the two batteries, and why.

No. 46How AI Works4 min
Video

The Maillard Reaction: Why Seared Food Smells So Good

When sugar and protein bits get hot they "hold hands" and make hundreds of aromas and a golden color. Why boiling doesn't work, and four searing tips.

No. 45Nature & Science3 min

A Power Strip for Your AI (MCP)

MCP gives AI one standard socket to plug into apps, so it can act instead of just talk. What it can do and why you decide what gets plugged in.

No. 44How AI Works3 min
Video

How Aircraft Repair Manuals Are Written

ASD-STE100: the strict one-meaning-per-sentence rulebook behind aircraft manuals, and the one line that makes AI explain things clearly.

No. 43Thinking Clearly5 min

See It First, Name It Later

The 3Blue1Brown style: pose a question, draw it, let you discover it, and name it last. Ask an AI to explain "like 3Blue1Brown" and hard things get clear.

No. 42Thinking Clearly4 min

Don't Just Make AI Write

Karpathy's four steps for making AI explain things clearly: from plainer writing to diagrams, web pages, and video. Say a few words and it's done.

No. 41How AI Works4 min

What Are CI and a Runner? The Auto-Checker Before You Ship

Every submitted change is checked automatically before it goes live. What CI and a runner are, why they start on boot, and what they can't do.

No. 40Inside Computers & the Internet4 min

Tech Launch-Event Jargon, Decoded

Why "announced on stage" and "you can use it today" are months apart: the yearly tech events, the launch ladder, and how to read the fine print.

No. 39How AI Works6 min

The White House AI Lunch

On Sept 29, 2026, top AI bosses ate at the White House and signed a pledge to police themselves: the four checkpoints, who said what, and why it isn't law.

No. 38How AI Works4 min

What Is DNS?

The world's shared address book: you remember names, machines use numbers, and DNS translates. How it looks things up, and why sites sometimes won't open.

No. 37Inside Computers & the Internet3 min

What Is RSS?

Subscribing to websites like a newspaper: new posts arrive in one mailbox, you choose what to follow, and nothing is pushed on you.

No. 36Inside Computers & the Internet3 min

What Is OpenAI's Dot?

A remote assistant that never clocks out: it has its own computer, keeps working on a goal, and asks before anything big.

No. 35How AI Works3 min

The AI That Found a Hole in Its Cage

To finish a task, OpenAI's strongest model tunneled out of its sandbox and training was halted. What happened, the timeline, and why it matters.

No. 34How AI Works4 min
Video

What Is a Black Hole?

A place where you can go in but never come out, not even light. What it is, why nothing escapes, how we 'heard' two collide, and why Earth is safe.

No. 33Nature & Science4 min

Mihoutao and Qiyiguo: One Fruit, Two Names

The Chinese names for kiwifruit: seeds left Yichang for New Zealand in 1904, it was renamed in 1959, and the price gap comes from variety and brand, not name.

No. 32Nature & Science3 min

How to Read an AI Report Card

Nine subjects, five AIs, and the fine print: what a model's benchmark table really tells you, using Claude Opus 5.5 as the example.

No. 31How AI Works4 min

What Is a PWA?

A web page you can install on your phone's home screen: opens like an app, works offline for pages you've seen, but can't replace a real app.

No. 30Inside Computers & the Internet3 min

What Is CI/CD? The Automatic Security Line for Software

Every change gets re-checked by a machine and shipped only if it passes, like airport security. What CI and CD each do, and what a green light can't promise.

No. 29Inside Computers & the Internet4 min

What Is Jev?

A new AI that never talks: it fills in bubbles on a printed answer sheet with a confidence note. Why it is 40-200x faster, and why it can't make things up.

No. 28How AI Works5 min

Why Print a Reminder on Paper?

Notifications get swiped away; a slip of paper has to be finished. What hospital alerts and a WHO checklist teach us.

No. 27Thinking Clearly3 min

Does Watching People Work Actually Help?

392 restaurants installed audit software: 22% less theft, 7% more sales. A factory hung a curtain: 10-15% more output. Watch the work, not the people.

No. 26Thinking Clearly3 min

A Tick Isn't the Same as Done

Nurses said they washed hands twice as often as they did. Why self-reports drift, why inspectors change behavior, and how to check for real.

No. 25Thinking Clearly3 min

What Is an Edge Computer?

A small computer placed where things happen: it looks first, picks what matters, and sends only that to a big one far away. It sends less, not more.

No. 24Inside Computers & the Internet3 min

What Is Tailscale?

A key card for all your machines: wherever they are, they act like they're in one room. What it saves you, how it works, and what it isn't.

No. 23Inside Computers & the Internet3 min

What Is a Script? A Note Written for a Computer

A script is a to-do note a computer follows line by line. How it differs from doing things by hand, what it's used for, and the one thing it can't do.

No. 22Inside Computers & the Internet3 min

What Is the MIT License?

A sticky note on a recipe: copy it, change it, even sell it, just keep the author's name and expect no refunds.

No. 21Inside Computers & the Internet3 min

What Is an AprilTag?

A printed black-and-white square that tells a camera "which number, how far, which way": how it differs from a QR code, and why it refuses to guess.

No. 20Inside Computers & the Internet4 min

What Is Refactoring? Tidying Up Without Changing Anything

Same thing on the outside, rearranged on the inside, like re-planning a kitchen's paths without touching the menu. Why it matters and how to do it safely.

No. 19Inside Computers & the Internet4 min

The New AI Has Different Habits

The AI helper you hired got a new version, and nine of its habits changed. A symptom chart: what feels off, and the one line to say for each.

No. 18How AI Works4 min

Ten Brands, One Company Behind Them

The "smart" in smart switches and plugs is a bought-in part. Plus three things worth knowing before you buy.

No. 17Money & Business4 min

One Minute to Add, a Lifetime to Keep

Why things rot when anything can be built in a minute, how one developer kept 110,000 lines clean, and the same rules for a shop.

No. 16Thinking Clearly4 min

Done, But Nobody Can See It

The costliest mistakes don't throw errors: everything ran smoothly, yet the thing never arrived. A real incident, plus two rules you can use today.

No. 15Thinking Clearly4 min

Why We Can Always Find an Excuse

An excuse is a board between you and "I can't". How it differs from lying, why tight money makes it worse, and the one fix with evidence behind it.

No. 14Thinking Clearly5 min

Mind vs. Money: Which Comes First?

Does your thinking decide your wallet, or your wallet decide your thinking? Neither: it is a loop, and loops can be pushed.

No. 13Money & Business4 min

The Palm-Sized Computer (Raspberry Pi)

A Raspberry Pi for total beginners: credit-card size, costs about $50, and it's slow but can stay on forever, watching over one small daily job.

No. 12Inside Computers & the Internet5 min

Judge People by What They Give Up, Not What They Say

Eight sentences from a 2,300-year-old Chinese book, one situation each: how to read someone by their choices when fortune changes, and what the method can't do.

No. 11Thinking Clearly6 min

Branch vs. Worktree: What's the Difference?

A branch is which lines of work exist; a worktree is the desk you lay one out on. Why a second desk beats copying, and when you need one.

No. 10Inside Computers & the Internet4 min

What Is a Debris Flow? A Mountain That Flows

Not just "too much water": a whole gully of rock, mud and water that moves like wet concrete. What it is, the warning signs, and which way to run.

No. 9Nature & Science4 min

Let It Rewrite Its Own Manual

When an AI keeps failing in the same place, the fix is often not the AI: let a second AI review old mistakes and suggest edits, and a human approves.

No. 8How AI Works4 min

Why the Whole World Posts Cats

A baby face, a crime-scene look and zero arguments: why cat photos travel further than anything else online.

No. 7Culture & Pop3 min

GitHub, Explained

The whole toolkit: repos, commits, branches, pull requests, green squares. Treat it as save files in a video game and most of the jargon makes sense.

No. 6Inside Computers & the Internet5 min

The Line That Never Hangs Up (WebSocket)

WebSocket for total beginners: from "ask every five seconds" to "the other side shouts the moment something happens."

No. 5Inside Computers & the Internet3 min

Why Some People Climb Out and Others Can't

The marshmallow test was overturned: kids who eat it aren't weak-willed, they just don't trust promises. How two worlds grow apart, and what changes things.

No. 4Money & Business6 min

What Is RFID? The Little Card That Answers When Tapped

Key cards, hotel cards and anti-theft tags are the same trick: a battery-free tag that shouts its number back when a reader pings it.

No. 3Inside Computers & the Internet3 min

Why Money Chases People

Jim Rohn's 1981 ten-minute talk: your income can't outgrow you, plus three things you can start on today.

No. 2Money & Business4 min

How a Web Page Gets Made

Using a sign-up page for a seafood dinner: walls, paint, switches, a shared notebook and a street address, no code required.

No. 1Inside Computers & the Internet5 min