[tpg]

If you're curious, the "dummy key" is a bump key. It's a relatively crude tool and is relatively hard on the lock, compared to traditional picking. There's also a certain level of professional pride, as you observed.

Hitting it with a mallet imparts force on the upper half of the pins, causing them all to briefly jump above the shear line, and at that moment the lock can turn freely without binding a pin.

A vibrating pick gun does essentially the same thing in a somewhat more controlled way.