Worms of Cologne

The Worms of Colón are parasitic worms that used to inhabit Fry's bowels. They entered Fry from a sandwich that he ate from a bathroom's vending machine, which contained their eggs. Once in his body, the worms immediately began to strengthen his body's systems. Fry got rid of them by threatening to kill himself, which would, in turn, kill the worms.

Trivia

 * The Lord of the worms claims that they are what "makes special sauce so special."