The Simpsons - Season 12 Episode 9

The Simpson family goes to an animation convention. Homer falls in love with a new product there and invests the family's life savings in a company that soon declares super-duper bankruptcy. To gain their life savings back, he sells his body for medical testing. The doctors find something odd in his head x-ray. Homer has a crayon lodged in his brain. This explains why he is such a moron. He thinks it is because he shoved crayons up his nose as a child. When the doctors remove the crayon, he gets smarter. This allows him to bond with Lisa. In fact Homer proves to be even smarter than she is. He is so smart that he accidentally proves there is no God. He also blows the whistle on the plant's nuclear safety violations. So the nuclear plant has to close and everyone hates him. He can't find happiness in things he used to like and he can't fit in with the people of Springfield. He decides to have Moe (a licensed surgeon) shove another crayon into his brain and he goes back to being a blissful idiot. Lisa understands why he did it and doesn't hate him for it.