Deliberate mistake: The fossilised dog looks like the dog did when he was young; it should look old and decrepit, as the dog was when he died. (Presumably deliberate, to avoid a spoiler.).
Futurama (1999)
1 deliberate mistake in season 5 - chronological order
Starring: John DiMaggio, Katey Sagal, Tress MacNeille, Billy West, Lauren Tom
Continuity mistake: When Fry falls into the cryogenic chamber his whistle drops right next to the chair. When it cuts, the whistle is gone. (00:01:50)
Lrr: I am Lrr. Ruler of the planet Omicron Persei 8.
Trivia: The part of Zapp Brannigan was originally going to go to Phil Hartman, the voice of Troy McClure and Lionel Hutz in The Simpsons, but was changed when he was murdered by his wife in 1998.
Answer: You are thinking about episode 20 of series 2 - "Anthology of Interest I". She technically never kills anyone, but in the episode she ask a "What if machine" (one of the Professor's inventions) what would happen if she was more impulsive. The machine then shows the more impulsive Leela killing off the Professor to get the money from his will and thereafter killing Hermes, Bender, Scruffy, Cubert, Nibler, Amy and Zoidberg to cover it up. Finally she does something really impulsive with Fry.
Andreas[DK]