Cas moans a tiny bit, then his eyes widen
Cas: R-Ren-
Cas: B-b-behind you...
Cas is frozen in place, eyes wide
Cas shrinks against the desk, hoping it'll just swallow him
Cas sits up and holds Ren's hand, squeezing it a little. Even though he's trying to hide it, he's clearly scared
Cas: Leave him alone, Katsuki...