I know this is years after the original posting but for reference anyway: I do believe it was the smashing of the skull on the floor, after falling through the trapdoor, that kills the victims - thus how the judge doesn't die straight away because there are several bodies already there that haven't been ground up yet; indeed, in one version of Sweeney Todd (though I can't honesty say I recall which one) their throats aren't even slit; they're just dropped down the trapdoor. Lordloss210