10 Creepiest Special Effects Ever Used In Movies

You'll struggle to find any creature within the Wizarding World who strikes fear into the hearts of Harry Potter fans quite like the ghostly prison guards known as Dementors - not including He Who Must Not Be Named, of course.

These floating beings literally fed on human happiness, and from the second they drifted into viewers' lives during Harry Potter and the Prisoner of Azkaban, it was clear these soul-consuming fiends were not to be messed with.

And hearing how the wonderful Alfonso Cuarón went about experimenting with the different ways he could create these creepy Potter creatures is almost just as gripping as the sight of the Dementors themselves.

The Gravity and Roma director initially played around with the idea of underwater puppets, shooting said practical creations in a tank in London (via Hollywood Jesus). However, that method, which involved capturing "really beautiful" slow motion shots of the puppet Dementors, wasn't practical to use for the flick.

But those tests did help inspire the metaphysical movement of the eventual CGI non-beings, with those puppeteering moments in the water being key in the creation of the Wizarding World's creepiest villains.