When: Season 2, Episode 2 Storyline: When the members of New Directions try to convince Mr. Schue (Matthew Morrison) to let them perform a Britney Spears number, it is soon obvious they have Brit on the brain. After several glee clubbers go under for routine dental work with dreamy dentist John Stamos, the laughing gas causes them to hallucinate about the pop princess. Why It's Great: Not only do we get to take a walk down memory lane with our favorite pop icon, but the entire episode also showcases Brittany's (Heather Morrison) killer dance moves! Channeling Britney's most memorable music videos, Glee successfully recreated the scenes, especially in "Baby One More Time" and "Me Against the Music." Spears' cameo proved that she was well on her way toward a comeback!