GNU
One example of an animal with an onomatopoeic name is the cuckoo, named after the sound that the male bird makes, "cuck-oo." Another example is the whip-poor-will, named after its distinctive call that sounds like "whip-poor-will."
rat
bee
gnugnu -----> gun
U => Ewe .... a female sheep B => bee ... not a mammal but an animal nevertheess,
Fox-Ox
The answer is PEEWIT
Ass
It is the gnu (often known as a wildebeest or wildebai).
An animal that has horns and a 3 letter name is an elk. Elks are a type of deer that can be found in North America, as well as Asia.
A name for a three-legged animal could be a "tripod."
The letters in "gnu" (wildebeest) can spell the word "gun."