From CCRMA Wiki
Piezo elements are used like a contact microphone. The material (crystal) forces electrons to move when it is shocked or vibrates. We connect two leads to it, which then can be amplified and smoothed with filters, making it more usable.
Motors can also be controlled my the AVR. There are some extra parts involved. Foremost of course is a DC motor. It also needs a motor controller, which supplies the needed voltage and current to the motor.
LED intensity, too!