A dog’s “grin,” with jaw closed, is submissive; as the mouth is opened, the arousal increases; and if the teeth are exposed, the look gets aggressive. Coming full circle, a wide-open mouth with teeth mostly covered—a yawn—is not a sign of boredom, as often assumed by analogy with our own yawning; instead, it may indicate anxiety, timidity, or stress, and is used by dogs to calm themselves or others. The ears can also go through these gymnastics: they can be pricked, relaxed and down, or folded tightly along the head. Eyeballing another dog directly can be threatening or aggressive; by
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