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Why the body and brain surprise us

Goosebumps without cold, a yawn that spreads, your voice sounding wrong the moment it’s recorded, that inner voice when you read, time seeming to speed up as you age: your body and brain play tricks whose backstage you rarely see.

This page gathers the whys of the intimate: perception, inherited reflexes, the illusions of everyday life. These are questions you ask while looking at yourself, and their answers owe as much to biology as to the way the mind builds our experience of the world.

Short answers, sourced, with no needless jargon. From skin to thoughts, here is a way to better understand the machine you live in.

At puberty the body clock shifts by hours: a teenager's sleep signal arrives late, then asks for a long morning to catch up.
Tendrille

Why do teenagers sleep so much?

Waking a teenager is a battle. Not from laziness: at puberty their body clock slides two hours late, and school refuses to follow.
Eyes follow the words, but somewhere in the head, a voice speaks them. Not for everyone: a meaningful share of people read in complete silence, and they often only realise it when they discover others don't.
Lumera

Why do we hear an inner voice when we read?
A reflex left over from a coat we no longer have. In the cold or under strong feeling, every hair gets pulled upright.
Lumera

Why do we get goosebumps?

Because we inherited a reflex built for a coat of fur we no longer have. Each hair is still hooked to a tiny muscle that yanks it upright in cold or under strong emotion: a leftover from when that actually did something.
The mirror does nothing: our brain invents the reversal. A visual metaphor, not an optics diagram.
Evelie

Why do mirrors flip left and right but not up and down?

Because they do neither. A mirror flips only one axis: the one running toward it. The left-right reversal is something our brain invents while trying to make sense of the reflection.
When you speak, you hear two voices at once: one through the air, one vibrating through your skull. A recording only keeps the first.
Lumera

Why does your own voice sound strange when you hear it recorded?
Each new year is a smaller slice of a life, and routine leaves fewer dense memories to look back on.
Chroneve

Why does time seem to speed up as we get older?

Because each new year takes up a smaller share of the life behind you, and because a brain settled into routine lays down fewer dense memories for you to look back across.