Rat baits are cruel and callous. As a wildlife Carer, all too often I get possums in that have eaten rat bait and by the time we have worked what is wrong with them it is too late. In the old days of cyanide death was swift. These days with the poisons used, an animal, depending on the amount it eats can take anywhere from 12 to 72 hours or more too die, the most horrific death possible. It cases internal organs to bleed out and after hours or days of suffering horrific pain their last gasps of air are usually followed by a gush of blood from the mouth followed by death.
The best thing I can compare the symptoms too, is like in the movie "Out Break" with Dustin Hoffman. At least in humans the symptoms can be diagnosed early. But the truth of the matter is that in possums it is not that easy to tell and because there is so many of them and they are not an endangered species there is no money available to test all of them. This makes it very hard to get help for them and lucky ones that we know for a fact have been poisoned are usually just put down, the unlucky ones suffer horribly until they die or hopefully we work it out sooner but even then it takes time to get them to a vet to be euthanized.
Not even a rat deserves to die that way. Disgustingly It would be kinder to nail them to a board whilst alive then put them out in the sun to die. Don't get me wrong, the way that rats and mice breed we have to do something to get rid of them but baits are not the answer. At the very least you should only use the ones that are in an enclosed trap that wild life can't get too. Even if you hate rats that much that you don't care how much they suffer, then bear this in mind, the claim that rats and mice go outside your house to die looking for water is largely crap! As a handyman I can tell you for a fact, every time your fridge does an automatic defrost it drops water in an evaporator tray below. I have pulled many smelly dead rats and mice out from under fridges and if they crawl up into the fridge lining then you either buy a new fridge or put up with weeks of rotten flesh smell. It is also a fact that these days in modern homes we use plastic water piping and it is not beyond a rat to chew threw them to get to the water and that leaves you with one hell of a repair bill.
In short there is nothing good about rat baits and to see a cute little baby possum die from one, would bring tears to anyone with a heart.