I did. How do you know that? You can't read the dog's mind and the dog can't talk to you. The dog could act in ways that you interpret as the dog being pleased, but trying to interpret it that way here would be circular reasoning since you are trying to show that the dog's actions show that things are pleasant to it.
What are you claiming -- that a dog is inherently unable to have "pleasant" feelings, or that humans have no capability whatsoever to judge the what's happening in the mind of a dog on the basis of its behaviour?
Another month, another rationality quotes thread. The rules are: