Cocoon

Cocoons are an invulnerable environmental hazard that is present in certain rooms, repopulating the room with enemies when the players are a set distance away. They cannot be destroyed or disabled. Cocoons were introduced in Rundown 005.

Appearance
Cocoons are bulbous brown sacs that hang from the ceiling.

Presumably, they open up to release more enemies when a room has been depopulated, this cannot be seen in-game though, as they will not repopulate rooms until players are outside the vicinity of the room it occupies.

Spawning
Cocoons only appear in certain rooms in certain expeditions, like Spitters and the Scout. They are dynamic in their placement however and may spawn in different rooms within the same expeditions.

Behavior
The effect of cocoons in a room is notable after the room has no prisoners in proximity from 2 rooms away. When these conditions are met, any enemies that previously occupied the room will have respawned. This creates a hazard in expeditions where rooms with respawned enemies have to be traversed several times or complicate escape extractions if the room intersects with the escape route.

Strategies

 * The presence of cocoons in the area warrants a stealthy approach, any ammo spent on killing enemies will be wasted if you inevitably have to backtrack through the area.
 * As long as one player is occupying the room the cocoons are in, enemies will not respawn. Note this option isn't viable if the objective requires your team to finish team scans.