Totality - a maths challenge

This is an activity from NRich.

Watch the video below (which has not got any sound). It shows two people playing the game.
Can you work out how to play the game?  
What do you think the rules might be? 

Have a go playing with someone in your house. Try it a number of times.
Can you find any good ways to win? Please let us know your thoughts using the comments box below.