Carnell first appears to deliver House's breakfast while Wilson is there. He makes it clear he is eager to please and will help out any way he can. When House jokes he's going to have sex with Wilson and then kill him, Carnell plays along by offering to cancel the morning maid service so they can have some privacy.
Later, House plays a prank on Carnell by playing a game of "William Tell" with a prostitute. Carnell protests but House seemingly shoots the prostitute in the abdomen. Carnell panicks until the prostitute starts laughing and Carnell realizes it's all a fake.