Game of Dumb Bell and Nail

This game simulates how a dumb bell hits a nail. When the dumb bell drops and hits the nail, the nail will go down by one grid, and the dumb bell bounces up, then falls again to hit the nail.

Exercise 1

Read the following code and understand how the game works

Exercise 2

Modify the game to make it funny. For example, the naughty nail might move left/right to avoid the hits.