Dogs are not quiet animals, even when they are doing nothing. The sigh that follows a long walk, the theatrical groan as they collapse onto a cool floor, the soft grumble before sleep, owners notice ...

The dog lies down in its basket, stretches out its legs, and sighs deeply. Many owners then wonder: Is my dog annoyed, sad, or just tired? A sigh can express contentment, relaxation, or tiredness, but ...