I think you’d better check out the definition of sentience before you start throwing the word around. If you had said that animals did not possess the power of reason, then you would be on somewhat firmer ground. Humans do indeed possess the power of reason, but frequently choose not to employ it. The notion that Man is created in God’s image is a pretty good example of this: no data supports it, nor does any data support the several assumptions on which it is based. It is an opinion, based on emotion, and therefore might be evidence of sentience, but not of rationality.
I have to agree that the cartoon is pretty silly, though.
Noise vs. communication