Episodes with recycled animation

All of the episodes that contain one or more uses of recycled animation, which are scenes and/or shots of previous episodes from the show that are used again, along with dubbing of new dialogue over the original.

This technique was very commonly used in episodes from Seasons 2 through 6 in order to save time and money in developing the animation for an episode. However, as of Season 7, it is no longer necessary to use this technique, and most instances of recycled animation after this point consist either of flashbacks or of reused fictional TV intros.