Do nothing

The knife hits you straight in the chest. You look down at the blade, and the black goo gurgling around it. Did it pierce your heart? Is that goo your blood?

You can feel every inch of the blade within you, but it does not hurt. Being undead's gotta have at least a few perks, right?

The girl lets out a panicked shuddered breath when she realizes that you're not going down. She has to stifle a yelp when you look up and meet her eyes. Describing her as terrified-looking would be an understatement.