Sympathetic resonance

Sympathetic resonance is a harmonic phenomenon in which a vibrating string can induce another unmoving string to vibrate without any physical contact.

The classic example is demonstrated with two similar tuning-forks of which one is mounted on a wooden box. If the other one is struck and then placed on the box, then muted, the un-struck mounted fork will be heard. In similar fashion will strings respond to the external vibrations of a tuning-fork when sufficient harmonic relations exists between the respective vibratory modes.