Why does the legendary fox have nine tails, and not eight or ten? This episode follows nine clues: a nine-headed snake in the Classic of Mountains and Seas, the way “nine” can mean “many,” the number as the top of the scale, a pun on “lasting,” Yu the Great’s nine cauldrons, Japan’s tail-by-tail ledger of age, Vietnam’s three- and six-tailed foxes, and why storytellers love a ladder. It ends with the answer the sources support and what they can’t tell us. Episode 17 of an animated series exploring East Asian fox legends, with the sources checked.