Firstly, I would like to say that, even if it were the case that no animal has yet declined the honor of being a sacrifice, this would hardly be grounds to assume that no animal will decline in the future. This is the magic of free choice and free will, that life is like a roulette wheel, where no assumptions about the future can ever be facts.

Fortunately, I am able to grant your request to see an instance of an "animal declining the dubious honour of becoming a sacrifice" from my own personal experience. It was 6 or 7 years ago, in fact during the Ashtan-Shallam war of my youth, that I was risking my life to maintain the notorious shrine that had been placed at North of Thera. On a lengthy journey to the Mhojave desert, I found three monitor lizards and offered them the choice of sacrifice. All three accepted, and followed me. During the journey back, I had the surprise of my life when one of them spoke to me! Alas, I didn't have the heart to take notes while we chatted so pleasantly, as he was a perfect gentleman, but I do remember his touching story about an ailing mother and family who needs him.
I remember distinctly that he asked me not to sacrifice him, although he seemed quite happy to stay and keep me company. Amused and touched, I was actually relieved that he had changed his mind, and I treated his wishes with utmost respect. I then offered to sethis two companions free, buthe informed me that theywere still intent on becoming sacrifices.

I hope this clarifies things.

Sincerely,

Echo

Penned by my hand on the 8th of Aeguary, in the year 226 AF.