The Honking - S3-E1
Audio problem: After they have welded Bender to the wall Leela and Fry leaves. When they go outside the door is closing. It cuts and we hear the door close but we can see the door is already closed. (00:11:45)
The Honking - S3-E1
Audio problem: When Leela welds Bender to the wall, she uses a gas torch. The sound effect is that of an electric arc-welder.
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]