How do they get all the sparkles in there?

This is the life of me. One time when I was little my mom sent me in to the bathroom to brush my teeth before we left to go somewhere. So several minutes pass and I am still in the bathroom. She walks in and I am intently staring into my tube of sparkly bubble gum flavored toothpaste. I looked up with great concern and ask her "How DO they get the sparkles in there?" And I have been trying to figure it out since...any ideas, let me know :)