While waiting for a consult, Dr. House is playing Metroid Zero Mission on his Nintendo Game Boy Advance SP. When Samus, the hero of the game, curls up into a ball in the hands of a larger being, House reacts as if it is "Game Over" and hands the game to the patient. She experiences the same game play/reaction and hands it back to him. Their reactions are not consistent with actual game play: what is occurring on the screen is actually a reward and a step toward completing the game, not a defeat.
When a patient asks House what he is doing, he replies, "level 4." The game he is playing is Metroid: Zero Mission. The way the game works is that the main character, Samus, travels in and out of various areas, guided by mysterious statues that tell her what to do. There are no such thing as "levels." In addition, the area he is currently in is Brinstar, the starting area for the game.
At the end of the episode, House seems to have found the gout medicine that resembles the cough medicine: small yellow round pills without an L printed on one side. The patient states his original "cough" medicine did not have the letter on them. The ones with the L on one side though are actually low-dose (81mg) aspirin pills.
While doing catheterization, the doctor sees the cardiac monitor and says there is an "ectopic" (ectopic beat), which means one premature beat followed by a long pause which would look like the distance between the pulse peak would be irregular. If you watch carefully you can see that the pulse is regular and no sign of ectopic beat.