If your dog is sopping wet after a bath or a swim, it’s only natural that they’d employ the time-tested shake to rid their fur of some of that water. But anyone who’s spent any time with dogs may have noticed that they sometimes shake in a seemingly identical way when they’re totally dry, too.

As This Dog’s Life explains, we don’t know exactly why this happens—but experts have observed the action enough to have formed pretty plausible theories. If your dog shakes after a nap, for example, it might just be their way of waking their body up after a period of immobility. “This is likely similar to what you do when you get up off your office chair: a quick stretch to get the muscles moving again,” dog trainer Kristin Benson told This Dog’s Life. It could also be a method of dispelling excess energy while in a state of excitement—like right before a walk—or during physical activity.

Not all shakes are great: It could also be a sign of stress. Say, for example, you see a couple canine pals punctuate a particularly rambunctious play session with a shake. “Although most of the time when dogs are playing rough, it’s fine for both parties, occasionally there seems to be an intensification that one or both dogs decide isn’t playful anymore,” Benson explained. In this case, the shake may serve as a self-imposed timeout.

Sleep, stress, and excitement are all normal parts of a pup’s life, so shakes are typically nothing to worry about. If you notice your dog doing the shake much more than usual, however, it could be a sign that they’re suffering from a rash or ear infection. In that case, a visit to the vet is your best bet.

[h/t This Dog’s Life]