From The Washington Post:
When its owner arrives home, a dog may seem to smile. When a dog wants to go for a walk, it may lift an eyebrow and look pathetic. These adorable expressions have helped create a “deep, long-standing bond between humans and dogs,” says Anne Burrows, a professor of physical therapy at Duquesne University in Pittsburgh, Pennsylvania. They also make dogs unique when compared with species such as wolves or cats.