Answer: Chocolate Syrup

If you’d been on set for the climatic shower scene in Alfred Hitchcock’s classic 1960 film Psycho, you’d have seen something a wee bit different than the movie viewers on the other side of the silver screen. The blood, featured so prominently and iconically in the scene, wasn’t a carefully concocted and properly red-tinted recipe closely guarded by the special effects crew: it was chocolate syrup.

Before the widespread adoption of color film, the color of movie props didn’t matter as much as the shade and consistency of them. As such, you could use props and special effects gear that clearly didn’t look right when viewed in color, but in monochrome it looked very realistic. Such was the case with chocolate syrup and simulated blood. Simulating blood, even today, is a tricky affair, but when rendered in black and white, chocolate syrup mimics the dark color of fresh blood, drips and spreads well, and has a distinctive separation when it comes in contact with water.

As such, chocolate syrup makes an appearance in many mid-century horror and thriller films shot in black and white. Not only was it cheap to acquire, it was easy to wash off, it was food-safe if actors got any in their mouths, and if you bought too much, well, there was always the potential for post-production ice cream socials.