You could color with them in the bathtub and they would melt away when you were done…
Because they were made totally out of soap!
My little brother and I were obsessed with these things.
The goal was to draw something SO good, the other person wouldn’t erase it when it was their bath time.
(I think the only thing that ever survived both of us was a Ninja Turtle fighting a Loch Ness Monster…)