Sorry, I just had to share what my niece said the other day.
My sister is not exactly Mustachian, but she's more frugal than most Americans. Usually she buy books from used book stores or library sales, so when they get home she always washes the books off (she's a bit of germaphobe). The other day, however, they took a rare trip to a "regular" book store. When they got home my sister just started putting the books away and her 4-year old stopped her and asked "don't we need to wash the books"?
It just cracks me up. And it makes me happy that my sister buys used books so often that her kid thinks it's normal to wash books.