These two children have filled up the bottle and the tube that is over the bottle. It begins to topple, but the girls catches it before it does. The boy and the girl take a measure of what they have done. There is still a little room in the top of the tube. They reach into the funnel because they know there are rocks in there. Are they thinking the rocks are preventing the tube from filling completely. They remove the rocks. The girl continues to keep the tube from falling. After removing the rocks, the boy lifts up the funnel. As he does, the sand starts to flow again into the tube. Both of them watch as the sand fills the tube. Their anticipation is palpable; just listen to them squeal with delight. It doesn't get any better than this.