The Insatiable (2007)

Revealing mistake: Sean Patrick Flanery plays a nerd who has trapped a female vampire in a cage. About 3/4 of the way into the movie, he tricks a co-worker into visiting, planning to feed him to her. He extends his right arm through the bars, and she starts to caress and kiss it, then begins to bite it and suck his blood. When he tries to withdraw, she tears off his arm at the shoulder. But in the next shot, he and Flannery both hit the floor outside the cage, and the co-worker's right arm is visible. However, when the scene begins, both Flanery and the co-worker are wearing watches on their left wrists, and in the shot of them on the floor, both have watches on the right, suggesting that the image has been reversed.