The episode, titled Work Bus, finds Jim once again messing with Dwight winding up with the entire Dunder Mifflin gang having to work on a bus for the day. To keep the cast cool while filming, the bus pulled a trailer with a refrigeration unit. The problem was that the show crew didnt pay attention to how it set up the refrigeration unit.

What they didnt plan on, they didnt think, Cranston said, that where the intake for the refrigeration system was, was exactly lined up to where the tailpipe of the bus was. So the exhaust of the bus was going right to the intake.

This story was first told by Jenna Fischer and Angela Kinsey, who played, respectively, Pam and Angela on The Office, in their new book, The Office BFFs. Though the title of the episode was Work Bus, the title of the chapter in the book is Death Bus, which Cranston took issue with.

Jenna Fischer actually saved everyones life, Cranston said. How? Colbert asked. Well, she said, I smell exhaust. Its coming inside the bus, Cranston replied. And Im thinking, Jenna, I mean, come on. How is that possible? Its not possible.

Though Cranston didnt believe Fischer at first, he checked it out for himself and realized that they were actually in real danger.

I got a chair and I stood up on the thing and I stuck my nose up in there, and sure enough, it was billowing down. It was carbon monoxide, Cranston said. I wasnt quite sure so I got a second wind, I got some more, I got nice and dizzy, and then realized, Oh my God, we could have all been dead. It would have been one hell of an episode. It would have been the finale before they would have planned that though.