In the episode where Fry becomes rich, when he comments that sardines would be the most delicious extinct animal they would ever eat (not likely
), and Amy comments that she's had cow.
But in the episode where they go the Slurm factory, the queen comments on how milk comes from a cow's behind (which isn't true, anyways).
(PS: Please forgive me for not knowing the episode titles. While I am a devoted Futurama fan, I don't know where I can find this stuff out. If anybody knows where I could, it would be helpful)