Continuity mistake: In Jack's first appearance to David in the hospital room, Jack uncovers the food on the tray and takes a piece of toast from another plate on the tray. The silver cover on the tray changes position throughout the scene in various shots. Sometimes the cover is resting partly on the tray and sometimes flat on the tray table surface.
Continuity mistake: In the scene where David (as a werewolf) exits the theatre, causing general havoc and mayhem, a car crashes into the one in front of it, sending the "driver" through the windshield. If you watch closely (or use slo-mo), you'll see that the driver goes through the windshield just before hitting the car in front of him (or her).
Continuity mistake: When David has his first transformation watch as his feet first start to change. His big toes grow and his pinky toes (what I call them) stay in place. Then when it shows David on his back. His pinky toes are the same length as his index, middle, and ring toes but his big toes haven't changed position just shape.
Continuity mistake: When David begins his first transformation, his nails turn into claws. At the end of the movie when David is sitting in the theater and going through another transformation, claws are seen sprouting from his nails.
Continuity mistake: Jack's friend, who he went to England with, appears to have a magic jacket. It changes colour twice during the movie: from blue to brown to green.