[ridgeguy]

To add to mschuster's great details below: remove all jewelry, watches, etc. when working with sources (even low voltage ones) that can provide very high current. In this instance, think of 12v lead-acid batteries that can deliver hundreds of amps into a dead short.

If the dead short path happens to be through your wedding ring, your finger can be deeply burned before your neuromuscular reflex can break the circuit.

[foobarian]

I found this out fidgeting with a 18650 cell in my pocket. (It was a salvaged cell without a plastic wrapper so all it took is bridging a few mm gap between the middle and the outer shell.)