The solar system a.k.a. "the flying chicken"

My fourth grader is studying the solar system this year.  It's really fun because he loves learning about it and I love it when he shares what he's learning with me because I find it really interesting.

We were talking about it tonight at bedtime and pondering why the planets are round (as opposed to other geometrical shapes).  Then he realized that squares couldn't rotate like circles.  It was an a-ha moment for him.

He says, "you know, the planets are like poultry in motion."

I say, "you mean poetry in motion?"

He says, "I always thought that meant something was like a flying chicken!"