Tony looks uncertain, but if Cesar's not going to hold a grudge over it he thinks it best not to argue.

"A blood sample? I guess, I mean I lose enough of it as it is a little more isn't going to hurt. What for?"

Oh Tony, so trusting. He finds the innocent look a little strange regardless, because to him it sounds casual enough that shouldn't even be necessary. Should he be suspicious? "Just be careful with it, yeah?" As far as he's aware his blood isn't toxic to anyone, but he'd still prefer no one get themselves hurt.