This is a pun from John Barnstead. It was published in alt.callahans a few years ago. (Yes, John, I still have a few of these left.) The term filk, as I understand it by the way, is used to indicate a modern song, usually a parody, done in a folk song mode.

Barnstead and Pernicious are looking forward to the WolfCon coming up soon in Wolfville, Nova Scotia, although they hope that their filksong version of famous forms of flatulence will not receive the response it did at the last con they attended. They didn’t mind the boos, and they could deal with the hisses. In fact, they incorporated them into their duet. But try as you might, you just can’t make a filk verse out of a Bronx cheer…