Click on the button on Mike Keith's page, and you'll be presented with two out of a potential one octillion sonnets, both of which are anagrams of each other. Here's how:
The two poems above each have the form of a classical English sonnet with fourteen lines of iambic pentameter and a rhyme scheme of abab cdcd efef gg. In addition, these sonnets are anagrams: each one can be formed by rearranging the letters in the other one. Every time you click the button above (or reload this page) you will see a different pair of mutually-anagrammatic sonnets - one of a grand total of about one octillion (1027) available.
This is made possible by having, behind the scenes, a text consisting of 14 sets of 10 lines of iambic pentameter. For each number n (from 1 through 14), we choose two different lines (say A and B) from set n then assign line A to the nth line in the left sonnet and line B to the nth line in the right sonnet. The resulting poems always have reasonable grammar and sense, as a result of the way the lines are worded; in addition, the fact that the sets as a whole obey the sonnet rhyme scheme (all lines in set 1 rhyme with all lines in set 3, and so on) ensure that the sonnets rhyme properly. Finally, the two poems are always anagrams because of this fact: all 10 lines in each of the 14 sets are anagrams of each other.
Read more complicated math stuff (sorry, that's the best I can do) about it at the link.
Link -via TYWKIWDBI