Anaphorisms
An aphorism is a short, clever saying which hold an inalienable truth. Anaphorisms are close relatives which are similarly short and pithy, but are in fact incredibly silly. Hippopotamus is a half way house, perhaps a hemi-anaphorism, since it makes sense, but, like the hippo and the poem, is essentially pointless.
Examples of aphorisms in poetic form include Needs Must about bald eskimos. It's also worth having a peek at their close relative, the Old Saws Resharpened, which include Weather Prognostications about global warming and a Christmas Was Coming, a festive number.