Balls roll down the track to change colour
Look at the colourful balls roll down a difficult track. First goes the green ball, it jumps, slides, squeezes through the track, only to find itself in a bowl of blue balls. In the end, the green ball turns blue as well. The red ball goes down the same track and jumps into a bowl of yellow balls. It becomes yellow, too. Lastly, it’s the blue ball’s turn. In the end it becomes pink.