I had wound my secondary, hooked up my rootbeer bottle capacitors, set up a spark gap with "L" brackets and stove bolts, wired up the car starter coil, and plugged it in.
It made a humming noise, but no sparks.
The air seemed alive. I looked at the neon circuit tester in my hand, and the bulb was glowing! Being the way that I am, I moved the tester closer to the top of the secondary. At about 3 or 4 inches ZAP it got me.
I can't remember (repressed memory?) but it must have arced out to the tester and to me. My arm involuntarily flung backwards, and the tester flew across the basement.
Later, I discovered that the way I wired it is called an "Oudin" setup, and is dangerous. Yes, I could have bought the farm right there.
Since then, the website I got those plans from has disappeared, which is good. I found more safety info, and have learned to respect the power of this device.