bzzt!

Specifically, my question regards safe-but-painful levels of electricity.

I'm a biologist by trade, so I know the theory: "It's the volts that jolt, but the mills that kill" - a large pd (voltage) across a nerve triggers depolarisation and actually creates a sensation, whereas it is the energy dumped into tissue (by flowing current) that actually causes damage. PD drops across the heart are a Very Bad Thing because it would rather like to decide for itself when to depolarise and do the whole blood-pumping, life-sustaining thing. High-power current across the heart is a Very Very bad thing because you kill bits of cardiac muscle to boot.

So, what I really want to know is: What's a safe amount of energy/current to dump into someone for electroplay? Has anyone here "done it themselves"? How did you do it? There are tonnes of designs out on the net for "shock boxes" and stuff, of the classic handshake-buzzer variety (I'm leaning towards a low-voltage capacitor into a transformer, roughly similar to the design on the Frugal Domme's site), but they don't seem to actually mention silly little things like what value the capacitors should be, or the turn ratio for the transformer...can anybody help?