[Her eyebrow shoot up in surprise; not at his horror, that's understandable from any caring person, but that he's actually shown it. He's always come across as so held together, to her, so far]
People have their own internal energy, after all. You have to know what you're doing to be able to tap that without taking too much, creating complications, and it's difficult to do with an unwilling party. Consent or no, though, it's still incredibly invasive... intimate. You're taking something from deep inside another.
Though, none of that would matter to someone who doesn't care if the person dies.