Continuity mistake: Before Iggy gets his horns, he got a shot of whisky in the bar from the blonde girl. The level of whisky changes between shots.
Deliberate mistake: During the entire movie nothing is mentioned about the rape of Merrin until the very end, even though it is quite obvious for a forensic investigator to determine she was raped, and something like that would be very important to help find a suspect. This is done deliberately to continue the plot as rape would make Iggy less of a suspect (being her boyfriend for years) and someone like Lee more (known by Iggy and others he had feelings for her).
Suggested correction: Boyfriends (and even husbands), are routinely accused of and found guilty of raping their partner. Given that they were seen arguing and told by the waitress that she saw Ig dragging Merrin to his car, there's no reason to think the police wouldn't suspect Ig of rape. We don't see any of the proceedings and we are told only a little bit of information about how the characters got to where they are at the start in order to build suspense, it has nothing to do with continuing the plot.
