WARNING: Do not try this at home!
Well, ok, if you want to go ahead, but don't say I didn't warn you =)
When I was looking at the cool lights at Spencer's Gifts at the mall this weekend, I also looked at the normal plasma balls along with the weird plasma light I got.
They have one that is smaller than the usual plasma sphere, but is much more powerful. When you put your hand against it, _all_ of the plasma bolts jump to that point, and the glass starts getting hot almost immediatly. This makes it uncomfortable to leave your hand there for too long, but it looks really cool.
One the shelf the plasma ball was on someone had dropped a penny, and I thought, hey cool! Pennies conduct a lot better than humans, so this would be a cool thing to use on the sphere! I picked up the penny, and touched the sphere with it, and a really bright bolt immediatly jumped to the glass, and you could see a little bit of glow actually projecting outside the glass where the penny touched, and it made a crackling noise.
This was really cool, though I was a little worried about hurting the plasma sphere, but it was just a demo model, not one I actually owned, right? =)
So then I had the bright idea of puttin the penny on top of the plasma sphere. I set the penny down in the exact middle, so it wouldn't slide off, and even when I took my hand away, there was still a bright bolt going straight up to the penny, which in retrospect was a little strange, since the penny wasn't actually grounded.\
But in any event, it was still making an kind of loud crackling noise, and I figured I didn't want to damage the sphere by leaving it on there too long (although I'll admit that the evil side of me was tempted to just walk away and see what would happen. =)
So I reached out to pick the penny up off the sphere, and as my hand got close, a small bolt leaped out from the penny and hit my finger. It hurt a medium amount, more than your normal static shock, but not anything really serious, and when I looked at the finger tip, there was a small white spot apaprently burned into it, since rubbing at it didn't make it go away. I managed to knock the penny off without further injuring myself by sweeping it off quickly from the side, but again, the evil side of me was tempted to leave it there as a suprise for others =)
So yeah, believe it or not those plasma spheres _can_ actually hurt you, but only if you're playing with copper and using a really powerful one.