When Alex walks down the stairs of the tunnel, the knot of her dress around her neck and her hairstyle change after the camera shows the sign "passage" and comes back to Alex's back.
La Tenia should not be able to breathe or move his jaw after being hit so hard on the head because of brain damage.
On several occasions (first noticeable in the opening scene when the 2 men are speaking on a bed), a light bulb will suddenly be "audible" or noisy when the camera films it.
When Alex is in the bed with her boyfriend and they get up to dance, the whole film crew is mirrored on the glass of the window.
Bellucci is obviously smearing fake blood on her face with her hand twice when hit by La Tenia.
At the party Vincent Cassel gives his characters name as "Vincent" instead of "Marcus." He quickly covers his mistake and saves the scene.
As the subway arrives, Pierre describes it as blue. Actually it is green and white.