It Follows- Loose Rules

From https://www.yahoo.com/entertainment/the-yahoo-movies-interview-it-follows-director-114138739632.html

You’ve said in other interviews that you didn’t set down concrete rules in terms of what the monster can or can’t do. But we do hear some rules in the film.

MITCHELL:  The only rules that we hear are rules that we’re told by a character within the film, who has access to limited information. If you look at the film enough, you can start to understand how he may be figuring these things out and how he has gotten the information that he has. But you also have to understand that they’re not rules on a stone’s tablet; they’re a character’s best guess about what’s happening to them. So, you know, they seem mostly right. But for me, that’s kind of fun, in that there might be some gaps in information, some things that he doesn’t understand and neither do we.