The double dactyl is, like the limerick, a fixed verse form -- and one that is often humorous. From Wikipedia's, we have this initial requirement: "There must be two stanzas, each comprising three lines of dactylic dimeter ( ¯ ˘ ˘ ¯ ˘ ˘ ) followed by a line consisting of just a choriamb ( ¯ ˘ ˘ ¯ ) . . ." As the samples below illustrate, a double dactyl involves both nonsense and multi-syllabic words -- a non-trivial challenge; visit Wikipedia to learn more.
The verses below are by Arthur Seiken, Emeritus Professor at Union College and I found them (with the help of editor Marjorie Senechal) in a 1995 issue of The Mathematical Intelligencer (Vol 17, No 2, p 11).
If you want to see more of this poetic form, here are links to follow: "Mathematical Double Dactyls" by Tristan Miller from the July 2015 issue of the Journal of Humanistic Mathematics and the Higgeldy Piggeldy verse collection of Robin Pemantle. And, again, here is a Wikipedia link that supplies formal details of these verses.