Let the Right One In (2008)

Continuity mistake: When Oskar intercepts Lacke's plan to kill Eli in the bathtub, Eli kills Lacke and drinks some of his blood, leaving some blood on her lips. She then kisses Oskar, which in turn leaves some blood on his lips. In the cut right after that the blood is gone from his lips. Later on it appears again, when he tastes it with his tongue.

Trivia: At the end of the movie when Oskar is traveling on the train with Eli inside the trunk, and they are tapping Morse Code on the trunk's lid, they are spelling out "P-U-S-S," which means "small kiss" in Swedish.