The children are instructed to pretend that they are a tree... planted in the ground. No part of their body is to move, not even if a gust of wind comes through the window! They then close their eyes and sit absolutely still for one whole minute. And when a minute has passed...
a shell is dropped into a metal bowl. And another. And another.
Their task is keep their mind focused on the shells that are dropped, counting silently in their mind. When all the shells have dropped, the aunty then says "Open your Eyes!" We then go around the room and ask the children. "How many shells are in the bowl?"
Not as easy as it sounds :-)
