After completion of the miniquest, the Rat's tail is unobtainable unless you are to kill a rat, complete the quest and pick it up. If the player shows a Rat's Tail to the Wise Old Man after completing the miniquest, he will tell the player to get rid of it. (Before completing he says "You have brought me a tail of a rat!" and "Yes, I think you should keep it for now.")
- For an exhaustive list of all known sources for this item, see here.