In the case of languages which have masculine and feminine genders, the relation between biological sex and grammatical gender tends to be less exact in the case of animals than in the case of people. In Spanish, for instance, a cheetah is always "un guepardo" (masculine) and a zebra is always "una cebra" (feminine), regardless of their biological sex. In Russian a rat and a butterfly are always "krysa" (крыса) and "babochka" (бабочка) (feminine). To specify the sex of an animal, an adjective may be added, as in "un guepardo hembra" ("a female cheetah"), or "una cebra macho" ("a male zebra"). Different names for the male and the female of a species are more frequent for common pets or farm animals, e.g. English "cow" and "bull", Spanish "vaca" "cow" and "toro" "bull", Russian "baran" (баран) "ram" and "ovtsa" (овца) "ewe".