How do you know how to play?
I think everyone playing had played the game when we were younger, and the rules are simple. You spin the dial and whichever the dial lands on, the person who's turn it is, must place their body part on the colour chosen.
What causes tension in this game?
Tension is caused as you want to know what the dial will land on when it is your turn. Once you are into the game, it gets much more difficult as it is harder to get into certain positions, especially when others players are on the mat. Tension is also caused when you have to wait in the position you are in, until your next turn.
How do you assess how you are doing? Do you get feedback?
You assess your performance, knowing how comfortable you are in the position you are having to hold until your next turn. Also once a player falls, they are out of the game, so seeing how many players are left in the game is another way you can assess how well you are playing. You can get feedback from other players telling you where there is any space for you to move. 
