Michael B. Jordan’s isn’t a typical supernatural horror flick as it incorporates a rule—the undead can’t enter a home unless invited. This doesn’t seem to be a random detail, as it plays a crucial role in the film’s suspense and storytelling, leaving fans wondering the reason behind it.

Here’s a lowdown on why the vampires in Ryan Coogler’s latest movie, Sinners, need to be invited in.

The idea that vampires must be invited inside appears to be rooted in folklore and pop culture. From Dracula to The Vampire Diaries, this rule seems to have been a staple of vampire mythology, and Sinners embraces it as well.

Early in the film, Jack O’Connell’s vampire, Remmick, approaches a house where Joan and Bert stay. Despite his menacing presence, he cannot cross the threshold until they unknowingly invite him in—a moment that seals their fate. Later, when Remmick and his clan arrive at Smoke and Stack’s juke joint, the brothers’ refusal to let them in keeps the vampires at bay.

The rule is explained by Annie, who warns the group that vampires can’t enter unless someone inside gives them permission. This makes the scene where Grace shouts for them to come in all the more terrifying, because once the words are spoken, the real horror begins.