Fallout: New Vegas
In combat, you do 75% more critical damage against animals and mutated animals. This perk will not affect abominations or mutated insects. It only affects creatures in the animal and mutated animal categories.
This includes all varieties of the above, such as golden geckos, pack brahmin, or Legion mongrels. Note that nightstalkers are not a type of coyote and are abominations, so they are not affected by this perk. Fire geckos, as well, are classified as abominations.
Fallout: The Roleplaying Game
When making an attack against a Mutated enemy with either the Mammal, Lizard, or Insect keywords, the attack gains the Vicious damage effect, if it did not already have that effect.