
Dogs have a bias that's easily read (probably because they aren't actively suppressing it). So if you want to know if a dog likes you,
just look at its tails:
When the dogs saw their owners, their tails all wagged vigorously with a bias to the right side of their bodies, Dr. Vallortigara said. Their tails wagged moderately, again more to the right, when faced with an unfamiliar human. Looking at the cat, a four-year-old male whose owners volunteered him for the experiment, the dogs' tails again wagged more to the right but in a lower amplitude.
Apparently, humans do the same thing, sort of. Maybe that's why there are more righties..