My husband's secret life

As anyone who has gone swimming with my family is aware, my husband is quite hirsute. So imagine my surprise last night when I discovered a 3" triangular patch of baldness in the middle of his back. Even more surprisingly, he doesn't know how it got there. Did he scratch himself while holding a razor? Did one of the boys get to him without his knowledge (although we are lax in some things, we do not let the boys play with razors, I swear). Is he having an affair and the other woman marked him as her territory by carving shapes in his body hair? The possibilities are...kind of the opposite of endless. I mean, how many ways can someone have their back shaved without their knowledge?