I was just playing with some rubber bands. They're the kind that come wrapped around the Wall Street Journal when it gets delivered at work, and they're fairly big: the circumference of them is 14 inches. For a sense of scale, one rubber band will just fit around a CD.
Well, I just put them on my arm, and they slid down almost to my elbow, and stopped. How odd, I thought. Why would they bind on my forearm?
And it struck me as I looked that my forearm was bigger than the rubber band could fit. Not my bicep, my forearm. My forearm is the same thickness as a CD.
I can't see it. If I hold a CD in one hand and hold it next to my arm, the CD is obviously bigger, until I actually put the CD on my arm.
They're the same size.
I don't know why that's so strange, it's just really unexpected.