A smile clues us in that a person is happy, but what about when an animal appears to be smiling?
Attributing human characteristics to animals is known as anthropomorphizing, and until recently, that’s what most animal behaviorists would say we were doing if we described a dog or other animal as smiling.
But new research reveals there's a possibility that some animals are actually expressing happiness when they "smile."
The idea isn't a new one. In 1872, Charles Darwin wrote about dogs that "grinned" and monkeys that "chuckled" when tickled.
However, modern science is still unclear on how much animals feel and what kind of emotions they experience.
Recent research at Emory University found that dogs have the capacity for emotion, and Nicholas Dodman, head of animal behavior at the Cummings School of Veterinary Medicine at Tufts University, says that dogs even have a sense of humor they express by "laughing."
A dog laugh sounds like a breathy forced exhalation, and a 2005 study found that when the vocalization is played at animal shelters, the shelter dogs' stress levels drop.
Dodman believes that scientists have been underestimating the emotional range of animals, especially more domesticated species like cats and dogs, and in the past decade, several theories have even emerged that "attribute primary emotions like fear, sadness, anger and happiness – and even some secondary emotions like jealousy and embarrassment – to animals," according to the Ecology Global Network.
Still, just because an animal appears to be smiling doesn't necessarily mean it is. In the animal kingdom, exposure of teeth can be a threat or even a sign of fear or submission.
Below, take a look at some happy-looking animals and decide for yourself: Do you think they're smiling?
Photo: Jordi Paya/flickr
Photo: Tambako the Jaguar/flickr
Photo: Jamie McCaffrey/flickr
Photo: Nicolas Connault/flickr
Photo: Alexander Granholm/flickr
Photo: Kamal Aboul-Hosn/flickr
Photo: Kelly Sikkema/flickr
Photo: Heather Paul/flickr
Photo: Ben Furneaux/flickr
Photo: Tim Simpson/flickr
Photo: Wayne Silver/flickr
Photo: Jin Xiang/flickr
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