Scratched vents

Scratched vents are a variety of wall trap that spawns 4, one from each of their faces, every 3 turns, so long as the scratched vents were visible to the player at least once. The scratched vents will indicate when they are about to spawn crabs by flashing the turn prior. If the vents are blocked on any of their 4 sides by a solid obstacle, such as a wall, that side will be unable to spawn chute crabs.

Scratched vents can continue to spawn crabs if their sides are blocked by an existing crab or other creature, by spawning the crab adjacent to the creature in the way. However, this cannot be done if they would have to place the newly spawned crab more than 3 tiles from the vents.

If the scratched vents are broken, rusted, or affected by EMP, they will cease to function.