When a female laboratory mouse is placed in a cage with a male, he pounces on her and bonks her a few times. But once the male is satiated, any further approaches from her are rejected. But should a new female — indistinguishable in our eyes from the first — be introduced, the male will pounce on her until, satiated again, he will reject further advances both from her and the first one. So the cycle continues, with the male interested only in new females.
This phenomenon is known as the Coolidge effect, after an episode from Calvin Coolidge’s 1924 reelection campaign. The President and his wife, Grace, visited a chicken farm, touring in separate parties. When Grace reached the farm’s prize rooster, the farm manager explained that the cock, er, covered 20 times a day. Impressed, Grace asked the manager to “tell that to the President, when he comes round”.
When Coolidge was told, he asked “same hen every time?” “Oh no, Mr President,” the manager replied, “different hen every time.” “Tell that to Mrs Coolidge,” the President said.