In the two scenes where Bender is crawling through the ceiling, you can see his wallet chain facing the camera.. Now while he may have two chains, it's pretty safe to say he's only got one. The scene was just filmed once and flipped around so he could crawl the other way. Not really a slip-up, more of an editing error.
In response to Mara's comment: because, audio and picture are two different things. You can separate the two and use one without the other. That is why there is music playing when Bender goes back to the closet, because they obviously couldn't have used the audio that was recorded with that shot.
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