Then there are the social aspects of caring for a dog. When you take the dog for a walk, you'll find many strangers who would otherwise have passed by without a word, now take the time to stop and coo over the dog. There's also a definite benefit it getting out in the open air and taking some gentle exercise with the dog, which helps to lift spirits and make people feel better.
This is so aptly summed up in that saying about shelter dogs: "Who rescued who?"
Training a puppy to help lift your mood involves two aspects. The first is general training so that he is well-behaved and to help you bond together. The other aspect is training him to come and apply gentle pressure to you, to make you aware of his physical presence, at times when you're feeling low or depressed.
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