No batteries required

She must've wanted to communicate to her brother, but how?

Cell phone -- nope, don't have one.

Walkie talkie --batteries are dead.

Walk over to his room -- too much effort.

Just holler across the hall --  nah. Been there, done that.

Having discarded most of the normal ways to communicate, the girl opted for this instead. 

A little bit of yarn tied together and strategically looped in just the right places and voila, a perfect message delivery system.  She wouldn't even need to leave her room. They entertained themselves for hours sending messages back and forth.  I kept hearing exclamations of how "awesome" this was. They could've been playing with all the computer, electronic and video games that they have, but no -- some yarn and a piece of paper.

No batteries required.