A Mugwump is a creature from the movie (and book) Naked Lunch. It is notable for, as Roy Scheider's character notes, "Mugwump Jism! It's aaallllll mugwump jism these days." Essentially, Mugwumps secrete strange pasty substances from their heads. They are replacements for typewriters, and if they like what you write, they secrete different sorts of intoxicating goo...no, really, I'm not making this up. I swear. Burroughs is much, much more damaged than I. Well, he was, at least.