¹     Light bounces off the things you see and reflects back to your eyes. You have two pupils. You have one in each eye. Pupils are the black circles in the center of your eyes. Your pupils control how much light enters your eyes. It is hard to see things when you are in the dark. The longer you are in the dark, the easier it will be to see things. Has your teacher ever turned out the lights in your classroom? At first it may have been really hard to see your classmates. Then your eyes adjusted. It got easier to see. With the lights off, your pupils are big. When your pupils are really big, they are dilated. Your pupils dilate, or expand, when you are in the dark. They do this to help your eyes let in more light and see more of what is around you.
 
²     Now your teacher turns the lights back on. You quickly shut your eyes .....
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