Horror movies are as much a mainstay of Halloween as trick or treat − but why are they so bloody?

Horror movies are plentiful in 2024, and plenty bloody. The year has seen the release of films awash in blood, such as “Immaculate,” “The First Omen” and “The Strangers.” With Halloween on the way, bloody offerings are streaming, in theaters and running in marathons on cable.

Watch them, and you’ll likely notice that as the decades pass, the directors, writers and studio executives of these films seem to produce more and more on-screen blood, violence and gore. But why?

As a professor of horror studies, I explore the depths of the genre with my students – and for us to understand the evolution of blood in horror cinema, we first consider how films reflect their times.

Alfred Hitchcock and Michael Powell created proto-slashers with “Psycho” and “Peeping Tom,” respectively. Both films were released in 1960 about four months apart, both feature serial killers, and both operate on a “tell, don’t show” visual aesthetic. Rather than show the blood to the audience, the films provide narrative cues to only suggest the blood.

In “Psycho,” Marion Crane, played by Janet Leigh, is stabbed to death in the famous shower scene. But the quick-cut editing gives only the illusion of her nude body being slashed as a small amount of blood washes down the drain in black-and-white tones. By not shooting “Psycho” in color, and avoiding the image of bright red blood in the bathtub – Hitchcock’s choice – the film doesn’t seem as violent.

By the late 1960s, the restrictive Hays Code, which prohibited overt on-screen violence and the use of fake blood, was replaced by the less stringent Motion Picture Association of America film ratings system. Filmmakers........

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