The Beast Must Die (1974)

The Beast Must Die is a 1974 British mystery horror feature film about several guests at a country mansion, one of whom will be revealed to be a werewolf. It was also released in the USA as Black Werewolf

Plot
A millionaire big game hunter gathers six people at his remote English mansion, announcing that he suspects one of them is a werewolf. The viewer is invited to unfold the mystery along with the characters. Near the end, there is a 30-second pause called the "werewolf break", where the audience is asked to guess the werewolf's identity, based on clues from the movie.