Or sort rocks as it may be? I had originally planned on using these rocks in the sensory tub along with some water to simulate a pond but as soon as I got them out Eva was at them. She started sorting them by size- big and small- and soon discovered some were neither big nor small. So she learned a new concept- medium.
Eva has returned to the tub various times throughout the day to touch and examine the rocks. I'm glad I didn't put the water in, because now she can play with the rocks whenever she chooses even if I am otherwise occupied.