There are a few slip ups that have to do with the same thing. In the episode where the mob is going to kill Lois, they go to the mob leader to ask him to call off the hit. You see him grating cheese. Then he takes out a cake. Why would anyone put cheese on a cake? Then Peter asks for a slice of it. That was the favor that Peter used (on the day of the mob leader's daughter's wedding, he will do any favor). The guy gives Peter the whole cake when he only asked for a slice. That is also a slip up. The last slip up is when Lois and Peter go back outside, Peter only has a slice of cake, not a whole one. Three slip ups in less than three minutes, go figure.