I really don't see sentience as something a creature either has or lacks. It seems to me that creatures have sentience in degrees, and that there are likely different sorts of awareness that together make up self-awareness. The only reason we can say with any certainty that other human beings are sentient and not just responding to stimuli is that we recognize it in ourselves and assume other human beings must be the same. (Although the extent to which we really are sentient and not just acting according to stimuli and weaving a comforting Story of Me after the fact is questionable, but we'll set that aside for now.)
That said, bacon is delicious and it's pretty important we be able to test on animals, so I'm a little conflicted.