The firmest airborne fox pilots within the latest dog.
Source text:

Nonsense percentage: %

 Nonsense the following:
Adjectives
Adverbs
Conjunctions
Interjections
Nouns
Prepositions
Pronouns
Verbs

How does it work? Lex looks up the parts of speech for each word and substitutes another, randomly. If a word cannot be found, the original is used.

(weatherbeard.com)