There is a kind of toy, which is called when you pinch it. What is the principle?

Extrusion is to convert chemical energy in human body into mechanical energy of toys, mainly elastic potential energy.

Mechanical energy is also transformed internally, and elastic potential energy is transformed into vibration kinetic energy.

The mutual transformation of elastic potential energy and vibration kinetic energy forms mechanical vibration, which propagates to human ears through medium (air) and causes electromagnetic effect, that is, sound.