Although he doesn't look pleased at the fact that Czes hurt himself, he doesn't react with anything other than his expression at first. He seems to have some sort of clear reasoning behind it, so Bucky leaves it alone for the moment despite his doubts.

The sight of the red liquid retreating back into the cut doesn't make him do much more than stare for several seconds, but after that, he lets out a breath and loses some of the tension in his posture, as if he's made a realization. He takes the knife back from the supposed kid.

"Every injury does that?" he asks, now well aware of how he could be an interesting experiment. Bucky has to wonder if HYDRA ever tested how quickly he could heal.