When one object is vibrating at the same natural resonant frequency of a second object, it forces that second object also into sympathetiic vibrational motion. So if there are two similar objects, and one of them is vibrating, the other will begin to vibrate as well, even if they are not touching.
A good example is two identical tuning forks. If you tap one of these forks on a hard surface so that it rings, its vibrations will pass through the air and cause the other tuning fork to vibrate. The energy from the first tuning fork has been transferred to the second tuning fork.