Franju states that he wasn't interested in the subject of slaughterhouses when he decided to make the film, but the location around the building was the Ourcq Canal allowing him to make a documentary film. Franju stated by using a documentary film format, he was able to use both locations as lyrical counterpoints and "to explain it as a realist while remaining a surrealist by displacing the object in another context. In this new setting, the object rediscovers its quality as an object".

Blood of the Beasts was made as a black and white film as an aesthetic. Franju states "If it were in colour, it'd be repulsive... the sensation people get would be physical one.

Source : Wikipedia