[ He might have shared some thought on the prison commentary - a report of the general feelings towards the place he's picked up on, the advice he's been given to make himself comfortable, the people who have spoken with more apparent displeasure toward the wardens, but the blood. That grabs his attention. He recoils there, in an unusually genuine reaction, furrowing his brow and curling his lip up. ]
Drinking blood? It's not completely unheard of, but it is unusual. Definitely inadvisable.
[ And quite obviously looking around with attention toward any glasses that enter his field of vision. ]
Though there are plenty of things that can look like blood - getting a good look at the viscosity would help, seeing how it moves and coats in the glass...