Critters are the tiny harmless creatures that can be seen in many different places in the caves.
They can be picked up and thrown like light objects, but don't cause any damage to enemies (with the exception of the Spiderling) and are mostly useless. They aren't usually worth paying attention to, but they are able to trigger traps which makes them able to affect gameplay.
Holding a critter will absorb any projectile that hits you from the front, such as arrows, much like an unconscious body.
Critters set off Arrow Traps, Tiki Traps, Powder Boxes and Mines, so can be used as decoys to help disarm certain traps. They are too small to be hit by the arrow launched from arrow traps, but will be killed by tiki traps. Critters are immune to explosions.
They can be killed with certain weapons such as the Shotgun or throwing corpses, and the blood splatter can help to fill up the Kapala if you have it. Small Fish are easy to kill for blood even without weapons by simply taking them out of the water.
Critters escape into the Shortcut house when each shortcut is completed. A Baby Frog escapes from the Jungle shortcut, a Penguin escapes from the Ice Caves shortcut and a Locust escapes from the Temple shortcut. Rats, Maggots, Spiderlings and Fish do not appear in the Gateway Cave.
Critters can't be taken through doors.
Critters have the lowest pickup priority, so can only be picked up when there are no other items overlapping them.