It's a Secret

Sounds are produced by vibrating objects. Vibrations are produced when something moves back and forth in a repeating pattern. With a cup phone, vibrations from your voice cause the cup to vibrate which in turn causes the string to vibrate. At the other end, the vibrating string causes the other cup to vibrate. These vibrations then travel to the air, then to your ears where it can be interpreted as sound. With the squawking chicken, vibrations travel from the string to the cup to the air causing to chicken to produces repeated squawking sounds.

Key concepts: sounds, vibrations, patterns, air, pitch, frequency