Continuity mistake: In the first episode of season 6, "Rebirth", near the end after the real Fry comes out of the Rebirth chamber, the robot Leela says that she and the robot Fry are in love she now has the real Leela's mechanical arm device on. But she never had it before or after that shot.
Futurama (1999)
2 continuity mistakes in Rebirth - chronological order
Starring: John DiMaggio, Katey Sagal, Tress MacNeille, Billy West, Lauren Tom
Continuity mistake: When Fry first meets Leela, there's a panel on the wall beside him. It has one red button at the bottom. In subsequent shots it has two buttons. (00:03:50)
Lrr: I am Lrr. Ruler of the planet Omicron Persei 8.
Trivia: The robot devil is voiced by Dan Castellaneta, the voice of Homer Simpson.
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]