The model is all physics.
4 walls turn slowly surrounding a ball and a stone.
The stone goes quickly through the wall.
The ball bounces for some time colliding progressively the walls then falls out.
I expect both stone and ball remain between the walls.
The ball has a circle collision mask.
Capx here
9giga.sfr.fr/n/50-26/f/633536588/deflate/no
Windows XP + Firefox