Michael's Second Disastrous Attempt At Surprise Planning involves an ill-fated telephone inquiry -- which he makes surreptitiously from his car -- into taking everyone down into a mine shaft. When it turns out that the industrial coal elevator isn't a free-fall and there's no laser tag once you get down into the mine, Michael loses interest. He insists in a TH that he thrives on improv. And he's wrong. See? I told you he had a lot in common with Robin Williams.
Dwight angrily emerges from his workspace to demand that Jim explain several suspicious diseases that have shown up on the questionnaires. In addition to leprosy and flesh-eating bacteria, people have claimed to have "hot-dog fingers" and a "government-created killer nanorobot infection." As meticulously crafted as that second one is, I think there's an argument to be made that nothing in this episode is as elegant and perfect as "hot-dog fingers," which makes even Angela laugh. In fact, everyone in the room has a horrible case of the giggles while Dwight is talking, which giggles they are desperately trying to hide from Dwight. Dwight says he'll be investigating (yay! I love it when Dwight investigates!), and until the perpetrator appears, "there will be no health-care coverage for anyone." Don't make him turn this PPO around, people. Because he'll do it.
Later, in the interrogation room Dwight has set up, he confronts Jim about, among other things, "Count Choculitis." Dwight tries to convince Jim to confess, but Dwight is no Brenda Leigh Johnson, so instead of confessing, Jim picks up Dwight's keys and locks Dwight in the workspace. Out in the office, Jim gives Dwight's keys a snap of the wrist, and they land in the shelving behind Stanley, who sees them go by and goes right on with his phone conversation. Dwight immediately calls Jim at his desk, and Jim's particular cheerful delivery of "Jim Halpert!" followed by his impish, happy "Who is this?" is probably the moment when he cemented heartthrob status for anyone who was still holding out. Dwight insists that Jim is fired, but Jim ignores him and takes an "unexpected" call from Pam in which they discuss the upcoming weekend.