"Do you believe that human beings can be reincarnated as animals?" And I said, "Yes." Most of the people who believe in reincarnation do not believe that, but in Judaism, at least in the Kabbalah, this belief does exist.
One of the ways in which mystical Judaism treats this is that sometimes you have to be reborn as an animal for a short time. The best job that you can do is to be reborn as a fish and to be eaten for Shabbos. That is the way the teaching goes. And there are marvelous tales about a Rebbe who eats up an entire goose one night because the person who was reincarnated in that goose needed the Rebbe to use the energy of the goose in prayer. And so he released him by eating him.
— Zalman Schachter-Shalomi, Wrapped in A Holy Flame