As for your suggestion:
I thought about that and tested it when i started building this game.
When the items stayed on screen after spawning the ninjaball, the game looked less like a game.
Thats when i realised i needed to make the items invisible and add a trail the ninja now leaves behind.
Using the black trail of the ninja, gamers can track down the movement when the items are back on screen again.
Just like a game of billiards.