Chuck runs in to the Gravitron and Leader follows him in. The door closes and Chuck hits the on button. If you have ever ridden the Gravitron, you'll get why this is a hysterical place to set a fight sequence. You cannot even move on this ride, let alone try to fight or run away. Both Chuck and Leader are plastered against the walls. Leader manages to climb on top of Chuck, but then the Gravitron stops, and they fall down, Chuck landing on top of Leader, knocking him out. He makes his getaway. That whole Gravitron sequence was very funny, which is probably why they named the episode after it, but I think "Chuck Versus the Carnival" would have been a better episode title, since they do so much more at the carnival than just fight on the Gravitron.
For example, as Casey and Sarah arrive, Chuck walks into a funhouse and gets confused when Jill follows him into the hall of mirrors. He asks her how she got into Fulcrum and why, and she says it was a leadership seminar at Stanford, and that once she realized what she was getting into, it was too late to get out. They are both looking around like they can't tell which image is the real person. She disappears mid-conversation and Leader walks in with a gun. Chuck starts running, but runs straight into a mirror. He comes face to face with Leader, who points the gun at him. Jill shoots Leader and they both leave. They run into Casey and Sarah, who arrest Jill despite Chuck's request that they don't hurt her since she saved his life.
Big Mike's telling Lester, Jeff, and Morgan what the plan is for Thanksgiving: He will lock them in, and doesn't care if that's illegal or if there's a fire while they're locked in. He is going fishing, and they will protect his store.
At the OOSSL, Sarah is asking Jill yes or no questions while she's hooked up to the world's most high-tech lie detector. It's high-tech in that it says "Positive" or "Negative" on a screen after she answers, but it's still not good enough to read any answers other than yes or no. I don't get that. If she's lying, why does it matter if it's yes or no, or some other answer? She passes the first few questions easily: Her name, Stanford, her degree in molecular biology. She says no at first when asked if she's a Fulcrum agent, but explains she's not used to telling the truth and then says yes. She knows where Leader is now, and then tells them where. Man, for an agent, she cracked easily. They ask her if it's a trap, and she says no. It says "Positive." They leave Chuck alone in the OOSSL, with Jill, who's strapped into a chair.