The Coolidge Effect

In short, animals do not choose their mates randomly. They identify
and reject those with whom they have already had sex. Scientists know
this reflex as the “Coolidge Effect.” It earned its name many years ago
when President Coolidge and his wife were touring a farm. While the
President was elsewhere, the farmer proudly showed Mrs. Coolidge a
rooster that “could copulate with hens all day long, day after day.”
Mrs. Coolidge coyly suggested that the farmer tell that to Mr.
Coolidge, which he did.

The President thought for a moment and then inquired, “With the same hen?”

“No, sir,” replied the farmer.

“Tell that to Mrs. Coolidge,” retorted the President.

[via kottke]