Blood of the Beasts is a 1949 horror short film, actually a documentary on French slaughterhouses, directed by Georges Franju. He directed Eyes Without a Face, and this short is included on the Criterion release of that film.
Horror News says it "was one of the earliest short films documenting animal cruelty" and "the film was directed to shock and disturb". FilmReference.com calls Franju "one of the cinema's authentic minor poets". It has no critics score at Rotten Tomatoes but has an audience rating of 94%.