Answer:
In a horror movie, suspense is often built up by the use of spooky music. The viewers often know that someone is going to die or get ripped up, or, at least, something is going to jump out because of the music that THEY can hear--and, of course, the characters cannot.
Because the viewers know something the characters do not, this is dramatic irony.
Another similar example is when the main character (in a scary movie), is being chased by a killer and we know that the killer is hiding in the closet but the character does not know that.
* I deleted "Cyrano de Bergerac," because it is NOT a horro movie.