Mule

Why is it just me finds this news flash funny? Why have I had to 'explain' it to everyone to whom I've read it aloud?

Let me test it on the 'A' crowd.

Little news paragraph on page 5 of Athen News for Jan 5:

Drugs at the border

Greek police near the border with Albania arrested two men allegedly trying to carry 400 kilos of hashish into the country on January 1.

One man used a mule to carry the drugs.

Er ... ?