Trivia: Betty Buckley really slapped Nancy Allen across the face during the detention scene. Brian DePalma wanted the right reaction.
Trivia: The smile that Damien gives at the very end wasn't scripted. Originally, Damien was supposed to "look really mean," but Harvey Stephens couldn't keep a straight face: he started to smile, then laugh. Richard Donner decided that the smile made Damien look even more evil, so it stayed in the movie.