I think - although I'm not sure - that Buddhist's transmigration (sp?) only involves human-to-human reincarnation. Hence the Dalia Lama reincarnation mythology. It's only the Hindus that believe you can come back as a frog or cow, I believe.
The fiction of the cycle of re-incarnation taking animal forms from snakes to baboons impels the query what caused the Tasmanian Devil to be born one? I think both Buddhism and Hinduism share this creed.
And I've always had questions about reincarnation. This is what I understand about it. With reincarnation, you keep coming back until you get it right and are then absorbed into the Universe, correct? If this is true, then why is the population of the world increasing, instead of decreasing? The other thing that's always bothered me is karma. If you come back and have a hard life, it's because you were bad in your last life. If you come back rich, famous...ect. It's because you deserve it because you were good. I think with this line of thinking it would make you feel, like you deserve it, very ego boosting, your all that on a stick. And it would make you less likely to help anyone who's down and out, after all, they deserve it.
All to say, when one's negatives - one's ignorance; overcones one's positives; there is at least; after death; the experience of becoming 'swamp grass'; or pond scum; or the experience/feeling of just hanging with the monsters who live in it. More than couple of realms to gravitate to - depending. . .