A tyburn is a six line poem consisting of 2,2,2,2,9,9 syllables. The first four lines rhyme and are all descriptive words. The last two lines rhyme and incorporate the 1st, 2nd, 3rd, and 4th lines as the 5th to 8th syllables.
scavenging beast, ugly, hairy, fat,
spreader of plague, filthy, dirty rat.