A Spanish Fly ?
This is a bilingual English/Spanish joke-- especially good for a class of native Spanish speakers. It also illustrates an important gramatical difference between languages (genders of nouns).
An Englishman went to Spain on a fishing trip.
He hired a Spanish guide to help him find the best fishing spots. Since the Englishman was learning Spanish, he asked the guide to speak to him in Spanish and to correct any mistakes of usage.
They were hiking on a mountain trail when a very large, purple and blue fly crossed their path.
The Englishmen pointed at the insect with his fishing rod, and said, "Mira el mosca!"
The guide, sensing a teaching opportunity, replied, "No, señor, 'la mosca'... es - femenina."
The Englishman looked at him, then back at the fly, and then said, "Good heavens... you must have incredibly good eyesight."
Link:
http://iteslj.org/c/jokes.html