Voltage conversion from 220V to 110V.

El...tingle? I remember working on an old ( tuber back as a teen in the mid sixties, dutifully keeping one arm behind my back to ensure not closing a loop. Two hours later I woke up 10 feet away on the floor, with a bump on my head.
Later I noticed a red scratch on my neck.
Next day I returned to my basement lair and saw a piece of 16 gauge dangling at head height from a waterpipe as my "convenient" ground. But recently I taught my daughter (17) how to replace a duplex while still "hot"; jeez, ya think I have a subconscious motivation to avoid all those tuition bills? PHEW!

A schoolmate of mine nearly killed himself (really) with a Heathkit Geiger counter. Although the construction manual warned about the high voltages he figured "four D cells...how dangerous can it be?" Well those D cells fed a chopper and voltage step up circuitry whch produced I don't know how many thousand volts, with substantial charge stored in capacitors.

As a high school science project one year I followed POPULAR ELECTRONICS' schematic to make a hand-held battery-operated "muscle stimulator" that sent unsuspecting holder's arm muscles rippling when both hands closed the circuit. Of course I had to get stupid and put a pot on its transistor-controlled transformer, allowing the thing to jangle the arms of as many as a dozen people linked in a circle! Needless to say I wasn't allowed to demo it live a second time...nor did it win a prize. Pretty damned scary for a pair of AA batteries though!