Children are familiar with real-world blocks and their interactions. An early play test with a few children examined whether a picked up block should float over and through all other objects until it is released is released into the world (and presumably made a part of a tower). An alternate system was tested whereby a selected block moved with the mouse but with physics and colluders working on it so that if it banged other blocks, they would move, if it banged the cliff it would stop, if it banged the UFO it might rotate, all under realistic control of 'the Unity physic engine'. This sandbox of block actions that behave like real blocks was found to be much more intuitive and appealing.