When the boy went back into class all of the other students were asking him to tell them some of his great ideas. The boy looked at them and opened his mouth and said: "Frog." Because the fly was in his brain all he could think of were animals and bugs. He tried again and said: "Horse."
Soon the fly realized that there was no air in the boy's brain because air can't get into brains, so he crawled until he came out of the brain and back into the boy's mouth. Then there was some air and he flew to the exit. However, he flew right into a bug catching bucket and died.