Fear moss was a type of predatory plant which would hang above water holes and cover mammals that came near, so as to live off their bodily fluids. It enjoyed the adrenaline and other chemicals that frightened animals produced, so it secreted a type of poison to ensure that it could consume these. When a Force-sensitive creature was affected by this poison, it would lose control of its fear and drift closer to the dark side of the Force. Such dark side creatures were particularly appealing to the moss, as it could taste the increased fear that they had. They were solitary and also Force-sensitive, being able to sense those who came near.