"Mule Balls" joke

Mule BallsAn American couple on vacation with some friends in Mexico were shopping at the market to bring back a few souvenirs to their family and friends. Time passed, and the couple realized that neither of them was wearing a watch. They noticed this little Mexican man taking a siesta next to this mule, which had the largest set of mule nuts they had ever seen.
Trying not to stare at the huge mule nuts, they asked the little Mexican man, "Excuse us, but could you tell us what time it is?"
The little Mexican man reached his hand under the enormous set of mule nuts and, lifting them high, said, "It's 3 o'clock."
Amazed by this, the American couple went off to find their friends and tell them the amazing story. "This little Mexican man over there can tell time by lifting his mule's balls!"
Curious and amazed, the friends wanted to see this first-hand, so they went back and asked the little Mexican man what time it was.
Sure enough, the little Mexican man reached out again, cupped his hands under the mule's nuts, lifted them up as if to weigh them, and said, "It is 3: 15."
The friends checked the time on their watches, and sure enough, the little man was correct.
Blown away by this, the American couple finally asked, "It is just amazing... how do you do that?"
"Do what?" the Mexican asked.
"Tell the time by lifting your mule's balls!"
"Ah...." said the Mexican. "I just need to lift his balls so I can see that big clock across the street."