The Day the Earth Stood Stupid - S3-E7
Continuity mistake: When Nibbler closes the door to the spaceship you see some of Leela's hair stick out. When it cuts her hair is gone. Then later it appear again. (00:06:50)
The Day the Earth Stood Stupid - S3-E7
Continuity mistake: When Nibbler bites the balloon and goes flying up, you can see there's a big open space between the "cream" booth and the "soylent chow" booth. And there's no curtain partition behind the booths. When he lands, the booths are right next to each other and you see the curtain.
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]