The word gnu is consistently pronounced in the song with two syllables as "g-noo", with the g clearly enunciated, and the n unpalatalised in contrast to the traditional "noo" or "nyoo".
He tells the story of a car – "great big flashy thing, with teeth; engine at both ends" – that is the bane of his existence, since it constantly occupies the one spot in the road outside his house where he can comfortably get from wheelchair to car and vice versa.
In the first verse, the singer is at the zoo when he meets a man who claims to know all the animals (like the habits of baboons and the number of quills on a porcupine), but misidentifies a gnu as a "helk"; the animal corrects him, further affirming that he is not a camel or a kangaroo, neither man or moose.
In the second verse, he has taken furnished lodgings, and wakes up in the night to see a stuffed hunting trophy above his bed; he is trying to decide whether the animal's head could be a bison, an okapi or a hartebeest, when he seems to hear a voice, asserting indignantly that it is a "g-nu, a-g-nother g-nu" and threatening to sue for its misidentification.
The jocular mispronunciation of "g-noo" in the song has led, through familiarity, to this becoming a widespread pronunciation of the word "gnu" in British English.