The answer to that will be dose dependent. If he eats a few grains of corn (like 1 or 2), he will be given tannic acid and put under full sedation until the convulsions stop. If he has something like a handful, they won't be able to do anything and he will wake up in the pond.

Either way, this would be an excruciatingly painful thing to do, well beyond the pain of most methods of dying. Its presentation could be strychinine poisoning or tetanus.