The tricky thing is that many behaviors that seem friendly can be misleading. “A wagging tail doesn’t always mean that the dog is happy,” says Ms. Stilwell. “Dogs will wag their tails when they are upset or over-aroused.” Similarly, if an unfamiliar dog rolls on its back to expose its belly, it doesn’t necessarily want to be petted. It might be asking you to move away.
A dog that attacks is often acting out of fear, says Ms. Stilwell. Those signs of fear may include a dog yawning, turning its head away when someone approaches, tensing up or staring.
Some dogs will slightly lift one front paw in what Ms. Stilwell calls “the anticipatory paw,” because it shows that they think something negative is about to happen.