In the news:
Dogs communicate different feelings with right or leftward tail wagging | Science | theguardian.com
"Dogs can tell how other dogs are feeling from the way their tails are wagging, according to researchers who monitored the animals' heart rate as they watched canine movies.
The Italian team found that dogs had higher heart rates and became more anxious when they saw others wag their tails more to the left, but not when they wagged more to the right, or failed to wag at all."