Bestial

A creature with this trait is animalistic, tending to behave instinctively rather than rationally. No matter how high its Intelligence score is, it is still bestial.
A creature with this trait never needs to make a Survival test whilst in its natural habitat.
Unless starving or desperate, a Bestial creature must make a Challenging (+0) Willpower test when frightened, startled, or injured. If it fails, the creature flees.
Dark Heresy - Core Rulebook - 134