A rat can swim for 72 hours non-stop. It can jump down 50 feet without injury. It can squeeze through a half-inch gap, leap three feet, climb vertical surfaces and walk along ropes. It can survive longer than a camel without water. It will eat anything that's edible and lots of things that aren't (lead sheeting, soft concrete, brick, wood and aluminium).
It reaches sexual maturity at three months. An on-heat female can have sex more than 500 times with a barnload of different males and produce 12 litters of 22 young each year. In short, rats are very, very hard to get rid of.
Tardigrades are plump, microscopic creatures that fall somewhere between worms and insects. Also known as water bears or moss piglets, they are the toughest animals on the planet. If their water supply dries out, they dry out, too. All life processes come to a complete stop and they become totally inert. In this "dead" state, tardigrades are practically indestructible: they have been frozen to within a degree of absolute zero (-272C) and heated to temperatures of 151C. They have been immersed in chemicals and squeezed by pressures six times greater than those at the bottom of the ocean: but, like living granules of instant coffee, with one drop of water they come back to life - even a century later.
"My ignorance of animals is legendary, but I know two dogs quite well."
Alan Davies