Many years ago when my dad was a professor of Electrical Engineering he really used a trick like this to teach the freshman about safety. After the "shocking" surprise he told the students the topic for the demonstration was "it's not the wire I touch that kills you, it's the wire *you* touch!"
As I recall he used a 12 volt setup - which of course everyone knows isn't enough to worry about - and a whole lot of amperage to vaporize a probe tip and make a really big BANG.
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"If they can't picture me with a knife, forcing them to strip in an alley, I don't want any part of it. It's humiliating." - windsock