Clark has not figured out the threshold yet, but Bruce has; his knowledge of a body - a human body - is second to none, in terms of what it can take, and what will result in a bruise, blood, or break. And he has catalogued in his memory every facet of Clark's skin and the muscle and fascia beneath, how it feels in this state, how much pressure it took last time to leave faint impressions of teeth and nails, playful red marks, or more serious purple welts.

There is something almost sweet in the way he takes his time finding a sensitive place on Clark's chest to sink his teeth into. He doesn't move very far down, really only bending slightly, as to keep them locked together below, rubbing and grinding against each other. He's so hard he's leaking with it, spreading sticky precome on the both of them. It's like a key in a lock desperately trying to twist open, tension coiling tighter and tighter. But it's more important that he get this patch of Clark's skin rosy, then darker, feeling thin and hypersensitive. A canine - not as pointy as the Kryptonian's charming shark teeth, but it'll do - catches on the worried flesh.

Not a vampire moment. Just barely.

Bruce raises his head, pushing Clark's arms up and back as he does, pinning them there with one of his hands on his crossed wrists. He pushes the thumb of his other hand into the welt he's made.

"Think you'll be able to come again?"