I imagine in a truly regressed state, as in not just roleplaying, he wouldn't understand the horny feelings. He just rubs his crotch against his pamp and hand and his teddy and pillow and his caretaker's leg because it feels good. He gets very fussy if he's pried away from the object he was just humping (dry or otherwise). But the face when he makes stickies in his pamp is entertaining enough for his caretaker to sometimes just let him go at it.