Cute Poison - S1-E4
Revealing mistake: Near the end, when Michael is unscrewing the sink before kicking the wall in, watch his hands in the foreground while he is talking to Sucre. Just when Sucre says "But what you were doing up there in the infirmary." Michael starts using his fingers to take the bolt out. You can see that there is no bolt, just him turning air, with a mystery 'unscrewing' sound effect. (00:39:35)