Why do we yawn?
Do you yawn when you're sleepy? Do you know why? All animals,
including people, need to breathe in oxygen and to breathe out carbon
dioxide. Sometimes your breathing slows down. You don't breathe
deeply enough to get all the oxygen you need and to get rid of enough
carbon dioxide. Scientists believe a yawn is a very deep breath which
brings in a lot of oxygen and expels a lot of carbon dioxide.
Most animals yawn. Scientists aren't sure, though, why seeing
someone else yawn can make another person want to yawn, too. Does
looking at these pictures make you want to yawn?