Between humans, a kiss on the mouth or cheek is a clear signal of warm feelings. There's no single definitive answer, though canine cognition experts have theories. "If we want to distill it down to one thing, it's communication," says Ellen Furlong, an associate professor of psychology and neuroscience at Transylvania University in Kentucky, where she studies dog behavior. Dogs are highly social and well-attuned to humans. If a pup is interacting with you, it's often with purpose.

They may not have the ability to speak our languages directly, but over thousands of years of domestication, dogs have likely developed certain'signals' to help them communicate with humans. When they're confronted with an angry face, a new study has discovered that dogs tend to their lips as an immediate response – and, this was more often the case when a human was involved, instead of another dog. Animal behaviour researchers say this may be linked to the dogs' perception of human emotions, acting as a way for them to communicate in response to visual cues of anger. In the study, dogs were shown two facial expressions (one positive and one negative, from the same individual). When they're confronted with an angry face, the researchers discovered that dogs tend to their lips as an immediate response Historically, animal's facial expressions have been considered to be inflexible and involuntary displays, which reflect an emotional state rather than active attempts to communicate with others.