In this section of Control guide you will find all the information about The Hiss. They are the main opponents of Jesse Faden in Control. These are amorphous beings that do not fit into the classical definitions of a living organism.
As mentioned above, the Hiss are amorphous creatures. They consist of energy capable of moving between dimensions. In order to survive, they are forced to absorb matter that they encounter on their path. Anyone who tries to interrupt the whole process will be attacked. The Hiss use people they meet to defend themselves - they take control of them and use their equipment.
One of the elements of the game is to correctly determine who was "possessed" by the Hiss. The most important symptoms you will encounter is the red glow around the character. Plus, their faces are starting to look more like skulls than living people.
Defeating possessed ones does not require any special actions. You just have to take away all their health points, whether using weapons or telekinesis.