[cartoon]

climbed a tree one-handed while holding a snowball the size of a bowling ball

Well, that's one of the correct answers.

Either that, or he built the huge snowball out of the dusting of snow on the branches. According to Calvin, it was Stupendous Man who carried the snowball to such a great height, and he didn't need a tree.
Artwork © Watterson/UPS; click for notice.