You know that phenomenon where someone hides their hand, puts a fake hand in a convincing position, and then someone injures the fake hand, and the first person actually feels it, even though they know it's fake?
Knives taking advantage of that. Knives methodically slicing off bits of Vash's prosthetic hand, delighting in his yelps of pain, secure in the knowledge that he's not actually injuring his beloved brother (well, only psychologically)
He can hit two birds with one stone: make Vash cry, and remove the human taint from him
-Rot, it/its









