This one is rather geeky; if you are not into poetic technique, it will disappoint you.
It is, of course (and you will instantly recognise), self-referential "Short Meter".
1. I love the hymns that put Two three-foot lines in front, And then bring in an extra foot To give the third a bunt. 2. With Latin prosody These learned authors thought It right to elide an "O" or "E" To achieve the effect they sought. 3. Nor was their work the worse, In that they had the nerve Their verbal order to reverse, And verbs for rhymes reserve. 4. How simple was their faith, These sober, staid, divines, Who buttressed an established Church With weakly founded lines, 5. And still maintain, today, When faith has more to meet, The even tenor of their way In odd iambic feet.
Source unknown, believed to be a Punch magazine from the 1950s.
Many thanks to John Laidlaw for providing this item.
Oh, and if you want an entertaining (although occasionally rude) introduction to poetic technique, read Stephen Fry's utterly brilliant and surprisingly deep The Ode Less Travelled, ISBN 9781592402489