This was a major hit with my two. We have done it many times. We froze some colored water in snack cups. When frozen, we popped out the ice cubes and put them in a tub. The kids poured in some water while I cut some yarn pieces. The process is simple enough, just place the yarn on top of a piece of ice then sprinkle with salt. The yarn will stick to the ice and you can "fish" out the ice from the water. There are a couple tricks that we have discovered. You have to use a lot of salt, let the salt set for a minute before trying to pull up on it (a good time to practice counting), and, it helps if the yarn is wet before trying to fish with it.