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.