What does a dog's tail wagging signify? [Article]

This interesting article on the NPR caught my eye - "The Tail's The Tell: Dog Wags Can Mean Friend Or Foe".

Dogs can pick up emotional cues from another dog by watching the direction of its wagging tail, a new study suggests. In a series of lab experiments, dogs got anxious when they saw an image of a dog wagging its tail to its left side. But when they saw a dog wagging its tail to its right side, they stayed relaxed.

While you may not be very interested in this, a vet called in to treat a rather angry dog might :)