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What do dogs learn
by sniffing pee?

Every pole is a mailbox
For anyone who’s curious
No. 82AnimalsPart 6 of 6Inspired by r/explainlikeimfiveFact-checked Oct 6, 2026
Video2:01 · English voice (AI) · English subtitles

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The full narration of the video.

On a walk, your dog stops every few steps and sniffs a pole forever. It isn't dawdling. It's reading its mail. Your nose has about six million tiny smell sensors. A dog's has three hundred million. Scientists estimate it's ten thousand to a hundred thousand times more sensitive than ours. A little puddle of pee carries the scent of the dog who left it. To other dogs, it's a signed letter.

So what's in the letter? First: who you are. One sniff and it remembers: an old friend, or a stranger. Second: male or female, and whether it's been neutered. Scientists let forty-eight Labradors sniff pee from dogs they'd never met. They spent longer on pee from dogs that hadn't been neutered. Third: whether a female is ready to have puppies. When a male finds that pee, he often licks it, sending the scent to a special little organ above the roof of his mouth to taste it more closely.

It even knows its own pee. One scientist followed his dog for five winters, secretly moving patches of pee-stained snow onto the path. Its own, it sniffed briefly and moved on. Other dogs', it sniffed much longer. So once it's read the letter, what does it want to do? Most often, it writes back. It pees a little on top of the other dog's mark, covering it with its own scent. The message: I was here too.

Males cover other males' marks more than females'. Small male dogs lift their legs extra high. So the mark lands higher. Scientists suspect they want to look bigger than they are. Before they ever meet, these letters have already told them most of what they need to know about each other. So next time your dog stops to sniff, don't rush to tug the leash. Give it another half minute to finish reading today's mail.

1

In one sentence

Every little puddle of pee is a signed letter. When a dog stops to sniff, it’s reading; when it pees on top, it’s writing back.

2

What you think
vs. what’s going on

YOU THINK
It’s dawdling,
sniffing forever
A few steps, a stop, and you can’t pull it away.
ACTUALLY
It’s reading mail
from other dogs
Your nose has about six million tiny smell sensors. A dog’s has three hundred million. Scientists estimate it’s 10,000 to 100,000 times more sensitive than ours.
3

What the
letter says

Who you areOne sniff and it remembers: old friend or stranger. Strangers’ marks get sniffed longer.
Male or femaleAnd whether it’s been neutered. When 48 Labradors sniffed pee from unfamiliar dogs, they lingered longer on pee from dogs that weren’t neutered.
Ready for puppies?When a male finds that kind of pee, he often licks it, sending the scent to a special little organ above the roof of his mouth to taste it closely.
Is it me?One scientist followed his dog for five winters, moving pee-stained snow onto the path. Its own got a quick sniff; other dogs’ got a much longer one.
4

After reading,
what does it do?

Writes backPees on top of the mark: “I was here too.”
Males cover malesThey mark over other males more than females.
Small dogs aim highA higher mark may make them seem bigger.
Meet before meetingThey know a lot about each other already.
5

A common myth

? The letter isn’t
magic
You’ll often hear that dogs can smell what another dog ate, how it feels, or whether it’s sick. There aren’t good experiments showing that yet, so we left it out.
Next time it stops to sniff,
wait half a minute
It’s reading today’s mail —
that’s how it gets to know the neighbors.
UP NEXT

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. 53 · 5 minKeep going →
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