[1] During a field trip in a museum exhibit about the human body, six-year-old Ian Alston is found to have bloody diarrhea.
She dismisses it as dehydration and gastroenteritis, but House, recognizing the symptoms and thinking this could be more than what she suggested, decides to drop out of the game (folding a pair of aces to Cuddy's bluff) and take the case behind her back.
Unable to determine what disease afflicts the two people, House orders immediate treatment to protect Ian's liver, which was the next symptom Esther developed.
Wilson, recognizing House's ongoing grapple with Esther's case, warns him not to become obsessed, using Moby Dick as an allusion.
Desperate and with only one remaining test, House wanders the hospital trying to think of his next move, when he hears from Wilson that he won the poker tournament.
Wilson won only because he had kept his hole cards, two aces, hidden the entire game, prompting House to have an epiphany.
The once-skeptical team is pleased when the test turns out positive, Ian is saved, and House finally discovers what killed Esther.