A happy beagle (小猎犬) called Bella loves Amazon boxes. It tears into them while ignoring other delivery boxes. Little Bit, a tortoiseshell cat, is similarly consumed — but by socks. It raids (偷袭) the laundry basket in the middle of the night and also paws through the open suitcases of house guests, who almost always find themselves missing a sock in the morning. Pets do some pretty weird things. But these strange behaviors often make perfect sense to the pets, said scientists who study animal behaviors. "These behaviors are not invented on the spot," said Carlo Siracusa, a professor at the University of Pennsylvania School of Veterinary Medicine. The pets are doing behaviors that their wild ancestors did, but they've changed them a bit to fit their new lives as pets.

Dogs can be trained to roll over and play dead. But their ancient instincts from their wolf ancestors are still there. Instincts, or instinctive behaviors, are behaviors that are done without thinking. They don't have to be learned. For example, some dogs will scratch the ground after pooping(排便). But they're not trying to bury their poop. They want other animals to notice it. "They are depositing smell in those areas," Siracusa said. "It's almost like drawing a picture with a big red marker around it," he added.

Cats, on the other hand, almost always bury their waste. "They are covering their tracks," says Monique Udell, an expert on human-animal interactions who works at Oregon State University. Cats are predators, meaning they hunt other animals for food. But other animals hunt them, too. So they don't want to be seen or smelled. Mikel Delgado, the founder of a California-based cat behavior consulting service, said that many other cat behaviors, arise from cats' wild origins.

While dogs share many behaviors inherited (继承) from wolves, they've also developed a few of their own. "Puppy dog eyes", the innocent look that many humans are helpless to resist, is one. Over the time period that they've lived with people, dogs have developed certain muscles around their eyes. This helps them make the adorable expressions that win over humans. Like wolves, dogs also like to lick faces. Humans think their pets are kissing them, but they are not. "It's how wolf puppies get food from their parents' mouths," Siracusa said. "It also can be a sign of submission. When a lower-ranking individual approaches a higher-ranking one, it gets down real low and licks the dominant one to say: ‘I'm not a threat to you. '"