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Dogs squint, making their eyes appear smaller, when they are in pain, stressed, or depressed. Depressed dogs may also be reluctant to make eye contact with anybody, even you. Of course, some dogs have "sad" eyes at the best of times, due to naturally droopy eyelids rather than depression, so exercise a little common sense when interpreting sad eyes as a sign of depression. Depressed dogs tend to display a lack of responsive ear movements to noises going on around them. For example, your dog may fail to prick up their ears at the sound of things that normally interest them, such as you calling their name, or their collar and lead being fetched prior to a walk. Licking or chewing their paws is a comfort mechanism for dogs, and can be a sign of depression. Depressed dogs tend to keep their heads lowered when standing or sitting. When lying down your dog prefers to rest their chin on the ground, and rarely raises their head in response to activity going on around them. When a dog is depressed, the tail is held down or between the legs and doesn't wag as readily. When you encourage your dog to wag his tail, the motion is subdued and half-hearted. Depressed dogs tend to stand in a passive way, with their heads down and tails lowered, barely reacting to encouragement. Your dog may give the impression of feeling sluggish, and will lack interest in what's going on around them. When dogs are stressed, they tend to shed much more heavily. If you pet your dog and your hand comes away covered in hair, or if you are suddenly having to vacuum much more often, your dog may be depressed.
Pay attention to your dog’s eyes. Observe your dog for droopy or pulled back ears. Watch for paw licking. See if your dog hangs their head. Monitor how your dog carries his tail. Be aware of your dog's overall body position. Watch for extra shedding.