Close one of your two eyes. Move your head close to the monitor and watch concentratedly to the left circle if you closed your left eye. You should look to the right circle if you closed your right eye. Keep watching and move your head slowly backwards while checking the other circle. What happens? And how is that possible?

Sarah and Mike conclude that it is wednesday. But five minutes later it is already friday. How is that possible?

Suppose you sit in a rubber boat in a swimming pool. In the boat lies a stone. You throw this stone from the boat into the pool. Will the water level in the pool raise or drop?