Possums, in general, tend to make few sounds and noises. They are quiet animals that avoid confrontation. It is usually said that they are gentle and docile creatures that do not like to attack other animals, like pets, and they also do not want to attack humans.
However, possums do hiss sometime, and that is usually when they felt threatened. When they feel threatened they produce a low frequency sound that is some kind of growling or hissing sound, although that sound is not usually lower than the sound that a pet cat can produce.
Possum babies also can create a little noise. They make a sneezing sound when separated from their mothers. That might be useful information for someone if possums have invaded his house roof or a garage. Also, adult possums sometimes produce some kind of clicking sound that helps them to communicate with each other. Those kinds of sounds can especially be heard while they mate. But if a person finds a possum that suddenly starts to hiss, the person should not be scared. Possums are probably even more scared by the presence of humans, so their hissing is just a defensive strategy, and they are probably looking for a way out. The other defensive strategy of possums is to lie down on the ground and play dead. That is what they do sometimes when they are dealing with another aggressive animal. So when the other animal leaves, they also leave, finding an escape route.
So, yes, possums do hiss, but they are generally quiet and will not make the sound very often. If you hear them hissing, it is probably because they feel threatened and want to defend themselves. You should back away from a hissing possum and give them some space.
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