It's not the shock that hurts, that just startles you. It's the banging your arm on the drill press that leaves a mark.
But yeah, bzg said the spark gap was hooked to the top, but if you look closely at the video, you'll see it's the other way around.
Not sure about this, I took the easy way and hooked up my SP-Gen to the flyback transformer and I can get it to spark at 16KHz, 5% duty cycle, but the spark sure seems small compared to his. Running from a 12 volt battery; drawing practically no current at all. So far I'm not seeing anything too exciting. Guess I need to keep at it.
Actually, I think my Slayer Exciter will do a far better job. It's air core and runs at a much higher frequency which Telsa indicates is key to extracting energy. Plus it uses a pancake coil for the primary which cuts back EMF.
Two things I need to find out by experimenting is frequency and size of salt water caps. Between those two items, I should be able to find something optimal.