This question was posed by "Freebird" one evening on the Appalachian Trail, as a bunch of us sat cooking, rinsing clothes, eating, sorting gear, and whatever else we did in the evenings.
Name 10 parts of the human body that have only three letters. Authentic words, that a doctor would use: in other words, "tit" and "ass" don't count. Nor does the one contributed last night by my 88-year-old mother, "nut."
OK, gang, have at it.