Under the Griping Beast

For a creature bound in fur so fine and soft as any down,
A monstrous appetite therein, though weighing scarce a pound,
I purchase chow and lettuce, I need scarcely mention why,
And when the fridge is opened it gives forth a piercing cry.

Under the guinea pig are shavings made of pine,
And to change them every week responsibility is mine.
But if I fail my duty there's a fearful price to pay,
For it stinks like Hell's own cesspit* till I throw the mess away.