A duck's quack doesn't echo, and no one knows why. Emus and kangaroos cannot walk backwards, and are on the Australian coat of arms for that reason. In every episode of Seinfeld, there is a Superman somewhere. Murphy's Oil Soap is the chemical most commonly used to clean elephants.
All porcupines float in water.
The reason firehouses have circular stairways is from the days of yore when the engines were pulled by horses. The horses were stabled on the ground floor and figured out how to walk up straight staircases. If you toss a penny 10,000 times, it will not be heads 5,000 times, but more like 4,950. The heads picture weighs more, so it ends up on the bottom. An ostrich's eye is bigger than its brain.