Card 52 of 82
The Coffee Drinker
A man in a bar complained to the bartender because his coffee had a fly in it. The bartender took the cup away, promising to bring a new one, and came back a few moments later. The man tasted the coffee and protested that it was the original cup with the fly simply removed. He was right, but how did he know?
Solution: He had sweetened the original cup with sugar. When he tasted the new coffee, he noticed at once that it was already sweet, so it was the same cup.