Pupil

(En español: Pupila)

Say: pyoo-pul

Pupils are in charge of how much light goes into your eye. That's why your pupils get larger in the dark (to let more light in) and smaller in the light (to keep some light out). You can use a small flashlight to test how your pupils, or your friend's pupils, change when the amount of light near them changes. It's all in a day's work for the incredible, shrinking, growing pupil.