A duck's quack doesn't echo, and no one knows why. That is why your TV set has channels 2 and up, but no channel 1. The only 15-letter word that can be spelled without repeating a letter is uncopyrightable. Emus and kangaroos cannot walk backwards and are on the Australian coat of arms for that reason.
Cats have over one hundred vocal sounds, while dogs only have about ten.
Camel's milk does not curdle.