Moira Shannon “Mo” Quirk (born October 30, 1968, in Rutland, England) is a British actress and voice actress. She is most notable for works on Nickelodeon in both the US and UK. She is most famous for being the co-host/referee on Nickelodeon GUTS and Global Guts. Her trademark quote for GUTS is saying "On your mark, get set..." and then blowing her whistle. After her GUTS career, she did some more work by doing voices of characters on different Nickelodeon and Cartoon Network cartoons. Mo also does voices in video games. She is married to Michael Rayner and they have two kids.