 Because the pin movements are highly elastic, the driver pins "jump" from the key pins for a fraction of a second, moving above the cylinder (shear line of the tumbler), then are pushed back by the spring.With no no other forces applied, the driver pins would come back to rest against the key pins once again, but the person applies a light rotational force to the key during the process and this causes the cylinder to turn during the short time that the driver pins are above the shear line, thus opening the lock.Lock bumping takes only an instant to open the lock.