Why does a head go into railings easily, but not come out?
and for grown-ups with little kids
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The full narration of the video.
A kid pokes their head through a gap in a railing to see what's going on. It slips right through. But when they try to pull back, it won't come out. Often the fire brigade has to be called to spread the bars apart. Strange. If the head got in, the gap is wide enough. Same head, same gap, so why can't it come back?
Did the gap get narrower? Iron bars don't move on their own. Did the head get bigger? No, it's the same head. Is it that you can't find the angle again? Going in, you tilt your head to find just the right angle. Backing out, you can't see behind you. That plays a small part. But it's not the main reason.
The real key is the ears on either side of your head. Look down from above. Each ear is like a little door. Its front edge is attached to the head, its back edge sticks out. Going in face first, the bar touches the front of the ear first. It pushes the ear back. The ear lies flat against the head and slides through.
Backing out, it's the other way round. The bar first meets the ear's open back edge. The ear gets pushed forward and folds over. Now it's doubled up and thicker. And it jams against the bars. The harder you pull, the tighter the ear gets squeezed, and the more it hurts.
It's like stroking a dog's fur. With the grain, it's smooth all the way. Against the grain, it all stands up. There's another way to get stuck. The body squeezes through first. But the head can't follow, and the child is left hanging on the bars. That's why American building codes say a railing gap must not let a ten-centimetre ball pass through.
If someone is really stuck, don't yank. Press the ears flat against the head and ease back slowly. If that fails, call the fire brigade. So, same head, same gap. Going in, the ears fold back with the push. Coming out, they curl up against it. Where did you get your head stuck as a kid? Tell us in the comments.
In it goes, but it won't come back
A child pokes their head through a gap in the railings to see what's going on. It slips right through. But when they try to pull back, it won't budge.
This is not rare at all. Firefighters across Britain are often called out to free a child's head, using spreaders, air bags or even saws to push the bars apart or cut them.
Same head, same gap
If the head got in, the gap is wide enough. So why can't it come back?
Iron bars don't shrink, and the head is the same head. Going in, you tilt your head to find just the right angle; backing out, you can't see behind you. That plays a small part, but it isn't the main reason.
Your ears are doors that only swing back
Look down from above. Each ear's front edge is attached to your head. Its back edge sticks out, pointing behind you.
Feel your own ear: press it back and it lies flat easily; push it forward and it curls up.
Going in: the bars press the ears back
Going in face first, the bar meets the attached front edge of the ear first. It pushes the ear back, flat against the head, and the ear slides through with it.
Coming out: the bars flip the ears forward
Backing out, it's the other way round: the bar first meets the ear's open back edge.
The ear gets pushed forward, folds over into two layers, gets thicker, and jams.
The harder you pull, the tighter the ear is squeezed, and the more it hurts.
Like stroking a dog the wrong way
Stroke with the grain and it's smooth all the way; stroke against it and the fur stands up. Ears are the same: they pass in the direction they fold, and catch going the other way.
Another way to get stuck: body through, head not
A small child's head is big compared with the rest of their body. Some gaps let the body through but not the head, leaving the child hanging on the bars. In research behind the US building code, some children's bodies slipped through an 8-inch (20 cm) gap while their heads didn't, leaving them dangling with their feet off the floor.
That's why the US home building code says a railing gap must not let a 4-inch (10 cm) ball pass through.
If someone is stuck, don't yank
Quick check
A head slips into railings but won't come back out. What's the main reason?
Ears are like little doors that only swing back: going in they press flat, coming out they flip forward, fold into two layers and catch.
