Jaw Bone is an unlockable passive item added in Booster Pack #5.
- Spawns a familiar that fires across the room in the direction of the first tear fired and returns to Isaac when it hits a wall, similarly to Little Chubby. Deals a flat 7 damage to enemies that come in contact with it.
- When thrown, the familiar will pierce through enemies if they are killed by the familiar, but the familiar will bounce back to Isaac if the enemy is not killed.
- The familiar will pass through obstacles.
- The familiar can retrieve pickups like The Boomerang.
- Blocks enemy tears when stationary and when thrown.
- After returning to Isaac, it has a short recharge time before it can be fired again.
- BFFS!: Familiar grows in size and does a flat 14 damage to enemies.
- Duct Tape: Jaw Bone will face in the same direction as Isaac and remain stationary as opposed to trailing behind him. Jaw Bone can still be fired.
- This item is possibly a reference to Judges 15:16 where Samson kills a thousand men with a donkey's jaw bone.
- Jaw Bone is possibly a reference to the movie, The Frighteners, where Judge chases a ghost hound who keeps stealing his jaw bone.
Concept for Jaw Bone (labeled as "Jaw") on the right side, along with other Booster Pack items and trinkets, by Edmund McMillen.