When you come home from work does your dog greet you at the door with a wagging tail? Does that really mean he's happy to see you? Dogs use specific facial expressions to show how happy they are to see their owners, scientists have found.

While most dog owners will recognize their pet’s wagging tail as a sign of joy, they may also want to pay more attention to their animal’s face the next time they walk in through the front door.

Animal behavior experts have found the animals’ emotions are betrayed by specific facial movements that can reveal whether your dog really is pleased to see you. Using high-speed cameras, the researchers tracked the changes in the faces of dogs in the moments they were reunited with their owners or when meeting a stranger for the first time. They found that the dogs tended to move their left eyebrow upwards around half a second after seeing their owner. When the animals were introduced to someone they had never met before, they moved their left ear back slightly.

Now, go home and watch your dogs facial expression. Are you a stranger to him or is he happy to see you?