Dogs, like other mammals, feel affect. No big surprise here. One way they appear to express affect is by wagging their tails. They apparently make larger tail-wagging movements to the right during pleasant events, such as seeing their owner, and to the left for unpleasant events, such as seeing an unfamiliar dog. The choice of side has been associated with brain activity: wagging to the right is said to mean relatively greater activity on the left side of the brain, and vice versa.
