This slip up happens towards the end of the episode were Fry wins the trip to the slurm factory. Bender, Fry and Leela have been caught, and Bender has been told he will be turned into slurm cans. After a while, when Fry has helped Leela escape, they rescue Bender. He comes out of the machine with a hole the size of can. Then, in the next scene, it is gone. Then, later, in the scene whan they are in the ship drinking slurm, Bender drinks his and it comes out the hole that has magically reappeared in Fry's mouth.