Yesterday DS4 collected a handful of small rocks when we were outside and then adamantly resisted the next activity we tried to get him to do. He got really upset and started yelling, "I need to do Valium experiments! Valium!" I asked what he meant by Valium and he explained to me, exasperated, that he needed to put the rocks in water and see how much the water level rose. "Ah," I said, "volume."