A few quotes I've always liked...
"If you take a dog which is starving and feed him and make him prosperous, that dog will not bite you. This is the primary difference between a dog and a man."
- Mark Twain
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"In the world which we know, among the different and primitive geniuses that preside over the evolution of the several species, there exists not one, excepting that of the dog, that ever gave a thought to the presence of man."
- Maurice Maeterlinck - 'Our Friend, The Dog'
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"Recollect that the Almighty, who gave the dog to be companion of our pleasures and our toils, hath invested him with a nature noble and incapable of deceit."
- Sir Walter Scott