The excess 9 knives are not needed to kill me, though I do get impaled and mutilated by the 10000 others.
I throw the last 9 knives at the next user, before faling over on the floor, and bleeding to death. After a day of lying there, dead, on the ground, my eyes are plucked out by Vultures, followed by the flesh in front of my stomach. The Vultures continue to eat all my bodily organs, before ripping my tongue out and flying home to feed it to their young.
The next user, having seen my empty carcass, turns and throws up, not expecting the knives that, somehow, are still flying through the air towards them.