On the Nov. 27 stop in Montreal of her Monster Ball tour, Lady GaGa was joined onstage by opener Kid Cudi. It's somewhat obvious that this collaborative stage performance would occur -- Cudi's "Make Her Say" samples Gaga's piano version of "Poker Face." And it's kind of funny to hear people in the crowd scream, "I knew it! I knew it!" when Gaga jokingly asks "who the fuck is on my stage?" as Cudi's drawl is heard over the speakers. One has to wonder if Kanye would have done the same if his tour with Gaga wasn't canceled -- he produced and added a guest verse to "Make Her Say," which appears on Cudi's debut, Man On The Moon: The End Of Day.