[Hmmmm...how to picture it...]

Imagine in your head how the inside of the tent looks like...and then pretend you reached with a hand and pulled from it like you're making it bigger with your own hands.

[Were he more knowledgeable about computers he'd compare it to grabbing the corner of an image and pulling from it to make it larger, but no, he's not great at computers. The metaphor never comes to mind]