Audio/visual unsynchronized: When Matt tells Luke he has to go to a funeral, his mouth doesn't match what he's saying.
Continuity: Matt shakes three sleeping pills into his hand, but in the next shot, there is only one
Continuity: In Chicago, there is only a light dusting of snow, but at the cemetery, there are two or three feet of snow on the ground.
Factual errors: There is never a vent between a restroom and another room - especially not in restaurant.
Continuity: When Matt is in Lisa's apartment and Alex is pretending to be Lisa, Alex sits down on the couch while Matt was sleeping. When she goes to kiss Matt as he is lying on the couch, he is wearing a white t-shirt. When he sits up to kiss her in the next shot, he is not wearing a shirt.
Continuity: When Matt and Lisa are making love for the first time, Lisa takes off Matt's shirt and in the next shot Matt is wearing his shirt.
Audio/visual unsynchronized: When Rebecca greets Matthew the first time in the restaurant she is heard to say, "Hey, Sweetie, how are you?" which does not match her lips.
Revealing mistakes: When Alex serves Mathew coffee in the champagne flutes, they both pick them up by the bowl instead of the stem which would be extremely hot to hold in their fingers.
Continuity: When Matt is introduced to Alex at Bellucci's he takes off his jacket and in the next shot takes off his jacket again.
Continuity: When fake Lisa is leaving her apartment after her and Matt slept together when he looks down at her from the window her car is, parked, facing left, on the far side of the street, after her day dream, her car is parked, facing right on the closer, opposite side of the street.
Miscellaneous: On the card that Luke gave Matthew, the number for Dragon Lady Shoes was 555 0123. However, when Lisa calls (and Matthew's in the shower) you can see the number on the painted windows of the shop, and it clearly states the number 555 0142 (or 555 0145). This is not the same as the card number.
Audio/visual unsynchronized: When Luke says to Alex, "Are we still going out tomorrow?" it is dubbed from, "Are we still going out tonight?" as his lips are mouthing the latter.
Continuity: When Matthew is confronting Alex in the restaurant when he realizes she isn't Lisa, his fringe alternates from being parted to the side and over his forehead between shots.