Chopped Liver only appears in the episode "Growth Spout." In the episode, the chopped liver is able to talk, as can the biscuit that was lying beside him in Mr. Krabs' cupboard.
Both have apparently gone unnoticed by Mr. Krabs for sometime. The chopped liver is mostly used as a gag only, for when the biscuit says "What am I, chopped liver?" The chopped liver says, "No, that's what I am."