Opossums & Deer:
Opossum
These are the ONLY North American marsupial. They are not related to rats. They grow from embryos in the pouch (2 months), to riding around on their mothers back as she teaches them the fine art of being possum-y for several more months. They do occasionally fall off, and then they need help as the mother will not return for them. If you find a fully haired possum baby less than 7" not including the tail, please call a rehabber for help. This is too young to make it on its own yet. Possums are not pre-disposed to rabies, but do use caution when dealing with them, as they will bite. If encountered with a domestic animal, and the possum appears dead, it may just be pretending as it is an instinctive fear response. Leave it be, and you should see it recover in a bit of time and able off on its own.
Deer
They are called Fawns. You may find them curled up in the grass all alone. Those big beautiful eyes staring up at you, pleading..DON"T TOUCH ME!! Seriously, their mother is nearby, watching. She leaves the baby alone and comes back to feed her regularly. Leave the area and make sure dogs are leashed. The mother will return when it is calm again. If it appears hurt, bleeding, or you know it was attacked, do call a rehabber for help.