So that's why he's grinning; Dolphins are the only other creatures who get pleasure from sex... and here are more incredible wildlife facts.
WE are a nation of animal lovers but how much do we know about our furry friends?
Follow our guide to mad animal facts and find out how much you never knew - and never really needed to.
A 1200-pound horse eats about seven times its own weight each year.
A bird requires more food in proportion to its size than a baby.
A cow gives nearly 200,000 glasses of milk in her lifetime.
A Hindu temple dedicated to the rat goddess Karni Mata in Deshnoke, India, houses more than 20,000 rats.
A newborn kangaroo is about one inch in length.
A flamingo can eat only when its head is upside down.
Dogs and humans are the only animals with prostates.
A duck's quack doesn't echo and no one knows why.
A rat can last longer without water than a camel can.
A woodpecker can peck 20 times a second.
All pet hamsters are descended from a single female wild golden hamster found with a litter of 12 young in Syria in 1930.
An albatross can sleep while it flies.
A chameleon's tongue is twice the length of its body.
A chimpanzee can learn to recognise itself in a mirror but monkeys can't.
An ostrich's eye is bigger than its brain.
At the end of the Beatles' song A Day in the Life, an ultrasonic whistle, audible only to dogs, was recorded by Paul McCartney for his Shetland sheepdog.
Camel milk does not curdle.
Crocodiles swallow large stones that stay permanently in their bellies.
A female swine, or a sow, will always have an even number of teats or nipples, usually 12.
Contrary to popular belief, animals are not all colour-blind. Many species, including dogs, horses and sheep, can distinguish some colours while the primates, especially chimpanzees and rhesus monkeys, have colour vision equal to that of humans.
Cat urine glows under black light.
During World War II, the very first bomb dropped on Berlin by the Allies killed the only elephant in the city's zoo.
It takes a lobster around seven years to grow to be one pound.
The bones of a pigeon weigh less than its feathers.
The hummingbird, the loon, the swift, the kingfisher and the grebe are all birds that can't walk.
The placement of a donkey's eyes in its head enables it to see all four feet at all times.
Dolphins are the only other creatures besides humans that get pleasure from sex.
A penguin only has sex twice a year.
A pig's orgasm lasts for 30 minutes.
The only domestic animal not mentioned in the Bible is the cat.
A bear has 42 teeth.
Many hamsters only blink one eye at a time.
A tiger's paw prints are called pug marks.
Reindeer milk has more fat than cow milk.
The Boxer dog was so named for his manner of fighting, which is that he starts a fight with his front paws like a human boxer.
Basset hounds can't swim. Their legs are too short to keep their very long bodies afloat in the water.
Dalmations are born white, their spots develop later.
Dog lovers with allergies should get a breed with with single-layer coats such as a Miniature Schnauzer, Kerry Blue or Italian Greyhound.
Dogs sweat only from the bottoms of their feet.
Dogs have about 100 different facial expressions, most of them made with their ears. Unfortunately, the likes of bulldogs and pit bulls only have 10, due to their breeding. Therefore, these dogs easily get misinterpreted by other dogs and often get into fights.
Cats respond better to women than men, possibly because women have higher-pitched voices than men.
A dairy cow can produce five gallons of ice cream a day.
A cow stands up and sits down 14 times a day.
The Ancient Egyptian word for cat was mau, which means "to see".
A cat's brain is more similar to a man's brain than that of a dog.
The scientific name of Mongolian gerbils is Meriones unguiculatus, which means "little clawed warrior".
A human year is equal to 25 hamster years.
Hamsters can only see up to six inches in front of them.
More people are killed in Africa by crocodiles than by lions.
Lions are also able to leap distances of up to 36 feet.
Tigers can't purr, only roar due to the shape of their vocal chords.
Tigers have a white spot on the back of both ears, which look like eyes. This tricks predators into thinking the tiger is looking at them. This is why they are called eye spots.
Elephants sleep standing up.
'A chameleon's tongue is twice the length of its body'
TONGUE TWISTER: A chameleon lizard, left PIC: PRESS PORTRAIT SERVICE