Early in the movie when Michael is in the bar drinking a beer the glass is nearly empty. When it cuts to Michael getting his head slammed against the table the glass is suddenly almost full.
Lowe wore a glove on one hand to smear blood on the wall of Michael's apartment. In the following scene, the glove switched hands.
In one scene, when Michael is talking to Howard, one of the lenses in his glasses appears to be cracked. In the next sequence where he is wearing his glasses, there is no crack in the lens.