An opossum looks allot like a rat in the fact that they have a rat like tail and a long snout. They are marsupials, which means that they have a pouch that the babies live in until they are fully developed. They can grow to be over 35 inches including their tail. They have 50 razor sharp teeth that they will be more than happy to show you as they hiss and growl at you, or any enemy. They actually will "play dead" if they are cornered and cannot get away. They will bite however if they have a chance.
The opossum is a very adaptable animal. They can live just about anywhere that there is food for it to eat and water to drink. They are natural climbers and use their long tail for stability while climbing. I do not know for sure if the full grown adults hang by their tales, but I do know that babies do.
The 2 opossums pictured at the bottom of the page were 2 of 3 that we had rescued when the mother was found dead. This was many years ago before I knew very much about animals. They were fed with an eyedropper at first, and then fed dog food. In the wild they will eat insects, small rodents, fruits and vegetables. They can vary greatly in disposition. One of the ones that I had was extremely friendly and could be held and handled with no problem and even seemed to enjoy the attention. (I do not recommend anyone try to go up to one (especially an adult) and try to pet it or pick it up. They do play dead, but they can bite and their teeth feel like 50 little razor blades !!!). Another one would growl, hiss, show his teeth and sway his head from side to side if you even got near him. Once they were old enough and big enough we released them out into the wild.
Please check out the links below for more information.

National Opossum Society
Nebraska Wildlife - Minks
Possum Network - Home to the Virginia Opossum