The “IT” in It Follows is an unknown supernatural force that passes from person to person after a sexual encounter. It takes the form of the last person “IT” had sex with.
Acting like a ghostly zombie PSA for STD’s it can take just about any form and won’t stop until it passes into someone else like a bad chain-mail case of herpes.
Out of an unexplained radioactive mist and odd cloud formation crawls a giant, multi-tentacled creature with a single huge eye.
It’s the first of many such monsters, but they’re nothing that some Molotov cocktails and aerial firebombing can’t contain.