A sudden, disorienting change of subject during a conversation, resulting in confusion among the other speakers.
Mike: "So, where did you go on vacation?"
Dave: "My wife and I took a cruise to Ensenada."
Harry: "I love that part of Mexico."
Mike: "Yeah, but how do you teach a cat to use the toilet.”
Harry & Dave: "????"
Dave: "Boy, that was a burk."
Harry: "Mike, you should warn people before you burk like that."