Then what is your defintion of sentient? It means to perceive, to feel, to be aware and to be conscious of ones self. Every animal is different. A cat is going to do cat things in a cat like way and just because it doesn't show emotions like a human doesn't mean it isn't aware or doesn't feel, it just shows it differently. Dolphins are a prime example of this. When you place a mirror infront of them, they will move their heads from side to side, open and close their mouth, do flips & just watch themselves. They are aware and they are not the only ones.
Besides that I agree with the rest of what you said.
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