I didn't know possums were immune to the baits, so I'm glad you mentioned it. And certainly not stupid. Quite the opposite in my book.
As for how anything but a rat got to it, that is not the point.........the fact is it did....and managed to drag it out to boot. And if the baits are left loose in a bowl or dish, even a rat could drag them out and move them around. They are known for doing that. So if folks are concerned that these poison baits could be moved out where something else could get to them, pinning them in place where nothing but rats and mice can get to them is essential. Easiest way to do that is to use a bait station designed for that use.
As for how anything but a rat got to it, that is not the point.........the fact is it did....and managed to drag it out to boot. And if the baits are left loose in a bowl or dish, even a rat could drag them out and move them around. They are known for doing that. So if folks are concerned that these poison baits could be moved out where something else could get to them, pinning them in place where nothing but rats and mice can get to them is essential. Easiest way to do that is to use a bait station designed for that use.