while engaged in doggy style sex, the *angry "rear" partner pulls out and quickly forces ANY piece of mail (regular mail, advertisements, boxed package) into the anal cavity of the front partner while saying "Drop your tail here's your mail"!!
Under ordinary circumstances the immediate, uncontrollable, unconditioned reflex is to drop tail.
*NOTE: the majority of the time the ""rear" partner has just received a piece of mail officially addressed to the "front" partner. The mail is always addressed from a secret lover.