The flinching is a good start, but then Tony's fangs slide out, and Bruce's reality concerns kick in again. If Tony's a vampire, he's going to want blood, and aren't fresh vampires especially hungry? Isn't that always the case? He lets go of Tony's shoulders and lays one on his thigh instead.

"It is happening though, apparently." It's important that he remind Tony that he can't drink from Bruce. What about Steve? Maybe Steve. He could probably take it, though Bruce doesn't know what his blood might be like. Ooh, Logan...

He's getting ahead of himself. Tony's panicking, and Bruce needs to stop his own brand of panicking -- i.e., planning -- to pay attention to him. He gently pulls on Tony's wrists.

"It's alright, Tony. We can deal with this. We can figure it out. You're not alone."