No. 9 - “Parasites Lost” (Season 3, Episode 2)
Fry is no Stephen Hawking by a long shot, but his severe lack of intelligence often works in his favor. In this particular instance, Fry was infested with worms after eating a truck stop egg salad sandwich out of a bathroom vending machine. However, this being “Futurama” and all, these were no ordinary worms, and begin to actually improve Fry’s body from the inside out. This includes healing him when he is injured, increasing his brain function and whipping his muscles into tip-top shape. And what else do you think Fry would do with his newly acquired “gift” but use it to win over the love of his life, Leela. He quickly does so, but then realizes he needs to know if she really loves him, or the worms that have made him who he now is. So, he sets off on a dangerous mission inside his own body using a micro-droid of himself (a la “Fantastic Voyage”) to force the worms to leave. After doing so, he goes back to Leela to see if she still feels for him the same way, but she quickly realizes she doesn’t. He must start again from square one, gradually trying to make the same improvements on himself the old-fashioned way.