Better to show from the front while you pull the string instead of hiding it as you did. Do it twice if you like to show everything from side and moving ball from the front. Would have made it far more instructive.
There is an angle from where the cotton enters the box directly over the glass when the cotton is pulled it drags the ball over to the glass and then lowered in
You can use a hot melt glue gun but I prefer PVA glue (white school glue) if you cover both pieces then wait a couple of minutes they will stick without the need for support.
