What is a water baby?

This kind of transparent ball, similar to a small bead and the size of a rubber pill, is mainly red, yellow, blue, green, purple, orange, black, colorless and cyan, which is very eye-catching. Packed in small plastic bags or small glass bottles, each bottle is about 15~30 balls, and the price is 0.5~ 1.0 yuan. Because they change magically when put into water, they also have an interesting name-"Water Baby".