What It Does
The line's signature — the decay, set and held where the hand says, and the arithmetic is the whole argument, and the one who cast it is the one who gave the blood. It is the poison school's answer to the fire school's cinder tongue: the rot does not burn, the rot waits, and the waiting is the one who wins.
The Cost
Circle 5 · Poison · Exchange: blood — casting time three rounds. On the ladder in The Veil, the blood rung is the price.
The Failure
The rot is set shaped, and the shape is not the one the hand sent — the decay is the one who waits, and the one who is waited on is the one the story is about.
In Stories
The archmage's poison spell; the one the camp does not cast twice, because the arithmetic remembers.
The door's scale anchor is Scorpion — the dragon casts it without thinking, which is how a reader learns the shape of the thing.