How did Harvey kill Jive in The Thief of Always by Clive Barker?

Jive offers Harvey a piece of pie, trying to tempt him, but Harvey refuses. Jive says "you think it's poisoned? well it's not, and I'll prove it". Jive eats the pie, and - to his surprise - he starts to disintegrate. When Jive asks what's happening, Rictus says "the pie, its reminding your belly of what your made of, dirt and ashes!"