The passage mainly explains

what causes goosebumps and why they are a leftover reflex (The passage explains the muscle that raises goosebumps and why the reflex is now a leftover in humans.)

What actually makes a goosebump rise?

A tiny muscle tightens and pulls a hair upright (The text says a tiny muscle at the base of a hair 'tightens and pulls the hair upright'.)

Why do goosebumps do little for humans today?

We lost most of our fur, so raised hairs cannot trap heat or add size (The reflex remains, but without fur the raised hairs 'cannot trap much heat or make us look bigger'.)

In this passage, a 'vestigial' feature is one that

once had a use and remains after that use has faded (The text defines vestigial as 'a feature that once had a clear use and remains after that use has faded'.)

The Reflex Behind Goosebumps: Level 3 Reading Comprehension Questions

When you feel a sudden chill or a wave of strong emotion, small bumps may rise on your skin. Each bump appears where a tiny muscle at the base of a hair tightens and pulls the hair upright. We call the effect goosebumps, though the muscles do the real work.

In furry animals, this reflex is useful. Raised fur traps a layer of air close to the skin, which helps hold in warmth on a cold day. A frightened animal with its fur standing on end also looks larger and more dangerous to a rival. The same reflex that warms can also serve as a threat.

Humans kept the reflex but lost most of the fur. Our thin body hair cannot trap much heat or make us look bigger, so the bumps do little for us now. Scientists call such a leftover trait vestigial: a feature that once had a clear use and remains after that use has faded. Goosebumps are a small reminder that our bodies still carry machinery built for an older, hairier way of life.

Comprehension questions