I have seen so many people use them interchangeably, and I think I've even seen dictionaries disagree about which is which, that I've pretty much given up on the words 'sentient' and 'sapient'.
Even though people use the words inconsistently, those people who distinguish them at all do so consistently, and you can use cognates to remember which is which: ‘sense’ = ‘feel’, so ‘sentient’ = ‘feeling’; ‘Homo sapiens’ = ‘wise man’, so ‘sapient’ = ‘thinking’ (more literally ‘discerning’ in the Latin).
I usually take it for granted that snakes are sentient but not sapient, although I don't really know enough about snakes to be sure of either.
But there's another idea, neither of which these words quite captures, that seems to be what really matters to Har...
Update: This post has also been superseded - new comments belong in the latest thread.
The second thread has now also exceeded 500 comments, so after 42 chapters of MoR it's time for a new thread.
From the first thread: