Banana juice

My Slovak girlfriend told me this today. I think it's an old one where she come from:

A farmer is riding his horse and cart through his village while carrying a large metal flask. A policeman sees this and stops him. "What's in the flask?" he asks suspiciously. "Is it alcohol? You know it's forbidden to ride a horse and cart while you're drunk."

"It's just Banana juice", replies the farmer innocently.

"I don't believe you", says the policeman, and grabs the flask from the farmer. He takes a huge swig, and grimaces at what he's just swallowed. "Urgh! That's disgusting!"

"It's just Banana juice", repeats the farmer.

"Doesn't taste like bananas to me", says the policeman, "but it doesn't taste of alcohol either. So I'll have to let you go."

"Thank you very much", says the farmer with a smile, as his flask is returned to him. Then he gathers up the reins, gives them a flick, and says to his horse, "Giddy up, Banana!"