This episode establishes the Professor and Zoidberg as good friends. This contradicts other instances in the past where the Professor is shown to regard Zoidberg in contempt, such as in Teenage Mutant Leela's Hurdles where, moments before he drowns, he shouts, "With my last breath, I curse Zoidberg!" Although, it could be argued that he was delirious at the time.
While Bender is performing the Third Kill Check on the Killing Machine, he uses the machine to make a salad. The axes on the kill wheel contained cyanide, which is poisonous. Despite this, the crew does not seem to mind. Later, they serve the salad to the professor and it does not harm him in any way.
It is possible, however, that since there were only 2 blades with cyanide on them before the salad is cut (due to Bender being the Third Kill Check), that the salad was cut by the blades without cyanide.