There’s a game Perry and Bruce learn at swimming lessons. They hold their breath, drop to the bottom of the pool, and act out a scene before they have to surface. They start playing it at Bruce’s pool at home.
When it starts, they both drop and make sandwiches, getting invisible ingredients out of an invisible fridge. Bruce is really good. His sandwich has three layers, and he toasts it before breaking the surface, gasping.
Then things escalate. They are fighting dragons, going to the moon. When Bruce builds a time machine and actually for real disappears, Perry gets worried.