A yrthak sees and senses exclusively through its blindsight ability, which is based on sound and movement - beyond 120 feet, it is considered blind. A deaf yrthak is effectively blinded as well except against adjacent foes - its weak eyesight functions enough for it to attack targets this close, although in such cases these creatures still gain the benefit of concealment (20% miss chance) because of the creature's poor vision. It is invulnerable to all sight-based effects and attacks, including gaze attacks.