[sev]

Interesting. What is that little gold-ish looking thing that moves from one pin to the other in this gif?

[tadfisher]

When you turn a lock, small machining defects mean that more load is borne by one pin than the others. Pushing up that pin while applying torque (using the allen wrench in the GIF) will cause that pin to be held up, which applies more load to some other pin.

[macalicious]

It's suppose to show you which pin is the correct one. The lock picker obviously can't know that's why he tries all of them.