If you trow away tow diferent firework stars, they stack together:
Exemple: You trow 1 firework star with twinkle efect, color red. And you trow at the same place another firework star, with color blue, and crepeer shaped.

When you pik them back up, you'll get:
1- Or 2 firework stars, with twinkle efect, color red.
2- Or 2 firework stars, with color blue, and crepeer shaped.