While he's standing at the sink, she's stabbing him in the back and also in the back of the head - because he is standing there, he is bleeding, and the amount of blood is indicative of a passage of time. The other pattern you see is this, on the mirror, blood spatter could come from blood in their mouth and getting hit in the head. Mr. Alexander was having some force applied to the back of his head. That's how you can know he was standing there at the time he was stabbed. But he's not dead. He begins to move in a different direction. He begins to go down the hallway. We know he's still standing.