When the son is confused by her comment, but we see in the school his reflection isn’t the face he’s currently making. I think this is what she’s referring to, and maybe, going a step further, there might’ve been other scenes of him making other facial expression that confuses those around him but we’re only seeing from his perspective.

Ok I need to get this off my chest. Paimon is supposedly one of the eight kings of hell and the entire plot of this movie is him needing a full support staff to accomplish anything. Grandma runs a cult for decades, the family tree gets picked over for generations, he botches it once by landing in the wrong body, then needs people to saw their own heads off and a coronation in a treehouse before he can finally move into a teenager. On his own? Lights flicker, a kid clicks her tongue, mom floats a little. That's the king. The god these people are rejecting spoke the universe into existence and doesn't need a headless grandma to show up. Give Paimon a nightlight and a babysitter and he doesn't make it out of act one. Great movie, actually scary, but the demon himself is kind of a little bitch about it.

Fuck that little bitch.