After the commercial, Foreman has the fastest-spreading case of Legionnaires disease ever and he is not happy about it. Cameron makes a very stupid comment, and Foreman insults her for it. She tells him not to be nasty, and he whines that he's in pain, so everything he says is totally excusable. Cameron points out that House is in pain, too. "And he's a delight!" Foreman says. "He doesn't try to kill his colleagues," Cameron points out. Eh, I don't know about that. He's certainly tried to embarrass Wilson to death more than once. Foreman's thermometer dings, and he shows the results to Cameron, who's pleased to see that his fever has gone down a degree since the Legionnaires started. Foreman isn't very pleased, though, and just makes his cranky old man face. But he has to admit that the pain isn't any worse than it was before.
Wilson stops by House's office, even though every time he does, he gets yelled at. House tells him that the Legionnaires has slowed the disease down, which he's hoping will give Steve more time to get sick. Wilson asks what House will do if Steve never gets sick, and that gives House an idea.
He strolls up to Chase and Cameron, and asks Cameron which diseases affect humans but not rats. "Why are you asking me that?" Cameron asks. "Because I'm sure that you spent the first twelve years of your life dreaming of being a vet," House says. Cameron does not deny this. Then again, you'd be hard-pressed to find a little girl who doesn't want to be a vet. Unless, like me, she's allergic to cats and dogs and, therefore, has to have a rat for a pet. House is asking because Steve hasn't gotten sick, and neither has Cameron. Chase says that there are some bacterial infections that can affect humans but not rats. Cameron says Foreman tested negative for every bacterial infection you can find in a brain. So now, House says they're looking for bacteria that doesn't affect rats and doesn't show up on tests, because the body won't make antibodies for it. It also explains why Legionnaires disease had a positive affect on Joe and Foreman, since it prompted the body to make antibodies that also fought the mystery illness.