Some one is selected to be Grandma and they position themselves at one end of room facing the wall.
Everyone else lines up at the other end of the room with the aim of creeping up on Grandma and touching her on the back without her realising.
Grandma can turn around at any time and if she sees anyone moving then she can send people back to the beginning.
The game is over once someone has managed to creep up and touch Grandma. That person then takes over as the Grandma.
The game can be made more complex by the following additions:
Introduce clothing: For example a hat, so that a person can only win if they touch Grandma wearing the hat. (This can create extreme competition between people or have the other affect of them working as a team)
Introducing an assault course: For example put a chair in the room and items of clothing laid out on the floor. The aim now is to get to Grandma but everyone must sit in the chair and put on a piece of clothing before getting to her.
Introduce the aim of touching Grandma in pairs or even threes. (This creates a lot more team work and cooperation as a group)
As a character: Choose a character or style that every body must get to Grandma in. E.g. as a cowboy, a Policemen, a sniper etc
Distraction: You can give people (Or Grandma) the task of reciting a poem or nursery rhyme throughout which tests peoples ability to multi-task.
Whilst the group is playing the game it is good to observe them and see how they respond to the rules and conditions you put on.
Also many interesting shapes and group tableau's can be thrown up. This can be used as a starting point to explore themes for stories and creating scenes.