1. The average dog has an intelligence level equivalent to a 2-year-old human. Thanawath Seangsuriyapone / Getty Images According to American Psychological Association, dogs can learn up to 250 words and gestures, which is equivalent to a toddler. 2. Dogs go poop when their bodies are aligned with the earth's magnetic field. Thamkc / Getty Images A study published in the journal Frontiers in Zoology found that dogs are sensitive to small variations in the earth's magnetic field. Under “calm magnetic field conditions,” dogs preferred to relieve themselves when their body was aligned along the north-south axis. The study also found that dogs avoid the east-west axis altogether. 3. Dogs have three eyelids. Squatchphotography / Getty Images Two of their eyelids are visible and one is hidden. The third eyelid sits in the inner corner of a dog's eyes and it has invisible tear glands. 4. The world's first dog lived 31,700 years ago and looked like a Siberian Husky. Chabybucko / Getty Images The prehistoric dog was about the size of a shepherd dog with a wide, but short snout and a wider brain case than a wolf. 5. Male dogs may lift their leg when peeing to make themselves appear larger to other dogs. Helenwalkerz65 / Getty Images According to a study done by researchers at Cornell University, evidence suggests that littler dogs lift their legs at a higher angle when peeing as a way to trick bigger dogs into thinking they are bigger than they actually are. 6. Dogs drink with the back of their tongue. Alex_ugalek / Getty Images Dogs don't have cheeks, so they can't create suction to drink like we can. Dogs move their tongues very quickly backwards to build up momentum which forces water into a column and up into their mouths. 7. Dogs instinctively curl up in a ball when they sleep to protect their vital organs and keep themselves warm. Diane39 / Getty Images If a pup sprawls out to sleep instead of curling up, it means they are simply hot or they feel very safe in their environment. 8. Dogs have 18 muscles that control their ears. Celiaaa / Getty Images For reference, humans only have six. They can rotate and tilt their ears to listen to sound waves efficiently. Their ears can also move independently from each other, allowing them to hear sounds in different directions. 9. A dog’s sense of smell is 10,000 to 100,000 times more accurate than a human's. Eudyptula / Getty Images Dogs detect odors in parts per trillion. That is the equivalent of a dog finding one dirty sock in a pile of two million clean ones! 10. Dogs sweat through their paw pads. PrzemysÃ âaw Iciak / Getty Images According to Pet MD, dogs have a type of sweat gland called merocrine glands, which are located in their paw pads. However, dogs rarely sweat through their paws. 11. Dogs can be trained to detect cancer and other diseases. Tomas Maracek / Getty Images In the human body, cancerous cells release different metabolic waste products than healthy cells. The difference is actually so significant that dogs are able to detect it. Dogs may also be able to sniff out cancer cells just by smelling someone's breath. 12. Dogs can get jealous. Wavetop / Getty Images Although dogs experience things like jealousy and envy, their emotions are not as complex as the emotions we feel as humans. According to the American Kennel Club, dogs are sensitive to fairness (for example, everyone being rewarded for their efforts), but not equity (for example, whether or not all of the rewards are equal). 13. A Greyhound dog could beat a Cheetah in a long distance race. Natalia Timchenko / Getty Images Although greyhounds don't run as fast as cheetahs (cheetahs can run up to 75 miles per hour), cheetahs can only run in sprints. So, in a long distance race, the greyhound would eventually outrun the cheetah. 14. A dog's nose is wet to help absorb scent chemicals. Ijdema / Getty Images Wet noses help dogs regulate their body temperature and cool them down because they don't have normal sweat glands like people. 15. A dog’s normal body temperature is between 101 and 102.5 degrees Fahrenheit. Sushiman / Getty Images According to Web MD, a temperature of more than 103 degrees Fahrenheit is considered a fever for a dog. 16. Dogs dream, just like humans. ÃËÃâ¬ÃÂ¸ÃÂ½ÃÂ° ÃÅÃÂµÃâ°ÃÂµÃâ¬ÃÂÃÂºÃÂ¾ÃÂ²ÃÂ° / Getty Images Human brains and dog brains function similarly during sleep. We both have the same type of slow wave sleep and rapid eye movement (or REM). During the REM stage, dogs can dream just like humans. If you see your dog is sleeping and you see their paws moving or twitching, it they are most likely dreaming.