Bruce backs up quickly, pulling his arms up to defend, but Thor's got about a thousand years of experience on him. The knife catches him on the chest--he's only able to push it back just enough to not get him in the heart, but it's in and it's going to be hell to treat if he gets out of this alive.

And right now, it doesn't look very likely that he'll get out of this alive.

He slashes with his knife again, trying to push Thor away, trying to keep him from pushing the knife deeper or moving it around. Hopefully keep him from pulling it out, too, but that may be a fair bit more difficult when keeping all the other things in mind.