The card trick that the magician does from his hospital bed with House is likely impossible to be performed in such circumstances in reality, being that it requires outside help. The trick is performed by forcing a particular card to be selected by the volunteer (there are numerous ways to do this), while the magician's assistant waits on the opposite side of the glass with a duplicate card. The magician turns the volunteer's attention away from the glass while the assistant affixes it to the other side, and then throws the deck at the spot where the card is affixed. In the flurry of cards hitting the glass (and resulting mess on the floor) it's very difficult to see that the card wasn't there before the throw.
The method by which it's suggested that Flynn would have escaped the water chamber, by regurgitating a swallowed key, is not the actual way this illusion is performed. The actual method involved dummy cuffs that open with the slightest bit of pressure, a pocket of breathable air hidden in the chamber's domed lid, and a magician with very strong leg and abdominal muscles. With a curtain drawn, he does an ab crunch inside the chamber to loosen the shackles on his feet and take a breath, and is usually again shown submerged moments later. After the curtain falls again, he loosens the wrist cuffs, does another ab crunch, and climbs out the top of the chamber. Despite safeguards, it is still a perilously dangerous trick.
Flynn is played by Steve Valentine. This is a strikingly remarkable coincidence, due to the fact that Valentine himself voiced and gave motion to the Uncharted 2 (A 2009 well-known video game) character Harry Flynn, which could indicate his appearance in the series as a precursor to his character in the game.
The trivia item below may give away important plot points.
A running joke of the series is that Lupus is almost always suggested as one of the possible causes of the patient's symptoms, although it is never the culprit (House even remarks that "It's never Lupus"). The reason for this may be that the disease has a wide variety of symptoms and can disguise other medical conditions. The joke is ended in this episode, when House comments that he finally has a case of Lupus.