Scientists know this reflex as the "Coolidge Effect." It earned its name many years ago when [US President Calvin] 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.org