This used to be just an article on Elizabeth Severino's website, on what the animals themselves taught her about dying, death and euthanasia. Now I see she's compiled it into a book, which you have to buy (too bad!). But I remember reading it a few years ago and finding it VERY enlightening. It became part of the basis for when I next had to decide when to euthanize, so I still recommend it. What she'd found out from the animals DID seem to bear out, when our own Sabin passed, on his own, so I then believed she'd heard the Truth from them. Here's the link to this section of her website:
Elizabeth Severino's Book