BLACK COWS

A political scientist, an engineer, and a mathematician are on a train that has recently entered Denmark.

In Denmark, the first field they see has a herd of black cows. The political scientist says, "Look! The cows in Denmark are black."

The engineer chides him. "You're careless. You should say 'The cows in this particular field in Denmark are black'."

Then the mathematician says, "You're both careless. You should say 'The cows in this particular field in Denmark are black on one side'."

Thanks to BooCat's sister-in-law, who is a mathematician.