How does custom melody music box work?

Custom melody music box works by inserting a perforated paper strip and cranking the handle.

How custom melody music box works

The paper strip has little punched holes which represent notes. When these little holes reach the music box mechanism, it flicks a particular string. If you keep cranking the handle, you will hear a melody. 

 Perforated Paper in Custom Melody Music box

Tip: in case the strip is not traveling while you crank the handle, you need to push the strip further for mechanism to catch it.