OK. near the beginning of the episode, Stewart tries to kill Lois (again) by shooting darts at her, but the cupboard door blocks the darts path and the door gets hit instead. SLIGHTLY later, it shows a broader view of the kitchen (this time with Peter in it as well) and during this time, you can see that the cupboard door does not happen to have darts on it. On another episode, Stew has to have Lois get an invention of his that she placed in a cupboard so this means that he could not have taken the darts out.

P.S. They didn't let me put in Stewarts well known name so I had to improvise.