It was weird to Hopper too. Maybe he had a leg up, having dealt with monsters in his world in the last few years. Still, he hadn't grown up with it - and the longer he was here, the more he was believing in all the weird shit, that every myth he'd ever heard was probably real.
"Think of them like... invisible electric fences. It's magic, spells and sigils and whatnot that keep the bad shit out." That was his understanding, anyway. He'd watch John do enough of them on their Dunwich-Fuckery-Only evidence room.