Is it true they play dead when spotted?
When I've approached them in the dark, they usually freeze and instinctively rely on their camo to remain undetected. .....very stealthy creatures.
Then when they think it's safe, they'll scamper off in another direction.
However, if they are spotted, they will sometimes growl. It was funny to hear what a fearsome low growl a young little female possum made when I approached her. If you touch them, they may bite. That's true of any wild animal.
If a predator were to bite them and not let go, they have an innate mechanism to skunk the aggressor, bite until let go and if that fails, they pass out/ faint.
This sometimes stops the killing instinct of the predator. If that happens and that animal smells the unpleasant odor, it might not have an appetite anymore. Then hopefully it will walk away and leave it alone. Minutes later, the opossum will wake up and go about it's business.
Another interesting defense mechanism opossums have is to sleep in a different location every night or two. They will come back, but only when they feel it's safe. Nocturnal predators often hunt by scent. If a possum's scent permiates one location, they are more likely to be found while sleeping. Opossums are smart and would rather make multiple safe houses so the bad guys can't find them easily. It might just be instinct that compels them to do this, but they are smart.
Fluffer learned to growl if she saw me coming. I didn't see her, but she saw me. If I got too close, that was her way of telling me to stop, so I wouldn't accidentally step on her foot or kick her on the path. She was talking to me so I'd stop and go around or let her leave. She is very smart.