In surgery, the other doctors tell Marion that he needs to contaminate Dr. Abramovitz, a.k.a. Popsy, before he's allowed to cut on the patient. He's a little taken aback.
Dr. Popsy, a very old man, makes a shaky cut and causes a big problem. He announces that he's contaminated himself and steps away from the room, leaving the mess to Marion and Deepak, the chief resident.
Marion and Deepak find a tumor in Dr. Popsy's belly, which Marion had missed when he did tests. He learns his lesson and feels terrible about it.