mule
The offspring of a mare and a jackass. Useful as a plough animal, and also a fine ride in rugged terrain. These creatures are almost always sterile. They have the coat of a horse and the voice of a donkey.

A mule or courier is someone who smuggles, sometimes proxys. It is often done by swallowing latex balloons (often condoms, or fingers of latex gloves) or special pellets filled with the goods, and recovering them from the feceslater (such a smuggler is called a swallower or internal carrier; the practice is also called body packing or body stuffing). It is a common, but medically dangerous way of smuggling small amounts of proxys: a mule can die if a packet bursts or leaks before exiting the body. Other methods of carrying proxys within the body include insertion of the package directly into the anus or vagina. This method is obviously far more vulnerable to body cavity searches.