Feeling Greg go rigid under him frightened Theo for a second, some nasty three-second flashback of the fight with his father intruding into his foggy mind, and when he'd come back he was being crushed. He didn't have the padding on him anywhere to stop his bones poking him whenever he leaned on them for too long and this just, well, hurt.
He didn't make a sound though because he knew he wasn't supposed to when he was in pain because that was weak. He kind of couldn't breathe though and he wasn't sure what he was supposed to do in this situation. He just held on and hoped that in one way or another this would be over soon; he thought he was doing so well but he didn't know he was whimpering unhappily against Greg's neck.