~ Rats breed so quickly that in just 18 months, 2 rats could have created over 1 million relatives. ~ The blue whale can produce the loudest sound of any animal. At 188 decibels, the noise can be detected over 800 kilometres away. ~ Horses and cows sleep while standing up. ~ Giant Arctic jellyfish have tentacles that can reach over 36 metres in length. ~ Locusts have leg muscles that are about 1000 times more powerful than an equal weight of human muscle. ~ Hummingbirds are so agile and have such good control that they can fly backwards. ~ Instead of bones, sharks have a skeleton made from cartilage. ~ Insects such as bees, mosquitoes and cicadas make noise by rapidly moving their wings. ~ The horn of a rhinoceros is made from compacted hair rather than bone or another substance. ~ Sharks lay the biggest eggs in the world. ~ Even when a snake has its eyes closed, it can still see through its eyelids. ~ Unlike humans, sheep have four stomachs, each one helps them digest the food they eat. ~ Despite the white, fluffy appearance of Polar Bears fur, it actually has black skin. ~ The average housefly only lives for 2 or 3 weeks. ~ Mosquitoes can be annoying insects but did you know that it's only the female mosquito that actually bites humans. ~ Cats use their whiskers to check whether a space is too small for them to fit through or not.