[Oh, good. He does have half a functioning brain. It's Snape's turn to recite back what happened as though reading a shopping list.]

He was gone, as you so succinctly put it, because Lily gave her life for her son. Potter - Harry - was protected by the love involved in that sacrifice.

[A beat. He swallows hard and glances away, having a slow look around the room - one which ends again at his hand on the desk. Finally:]

If you save her, everything changes.