Nick absentlly grabs a bat from the pack that are swarming and makes a tiny wound with one fang before taking a sip...and it tells him what he needs to know.

He flys between Mina and Meg before addressing the largest conglomeration of bats.

"Mina, really. This is foolish and uneccessary. Please stop before you hurt Meg or Val or anyone else. I like you. I don't want to have to hurt you."