The Revenge chance on harm stat is the chance an animal will turn manhunter when harmed by a member of your colony. It is three times higher for close-ranged attacks, like that of a machine pistol. For an animal like an ostrich with a 100% revenge chance, it will always turn manhunter after being hurt. Most animals also have a revenge chance on tame fail stat which dictates how likely the animal is to attack after a failed taming attempt.