Ethan came to the clinic because he had dark grey marks on his fingertips. He was seen by Gregory House. Ethan told Dr. House he thought it was frostbite, but Dr. House asked the patient if he had been in extreme extended cold (which he hadn't) and noted that the symptom looked nothing like frostbite. He told Ethan that he should probably take a long vacation before his boss found out he had been stealing money. Dr. House recognized the stain as silver nitrate, which had probably been mixed with petroleum jelly and put in the cash till to catch the thief. Ethan's reaction showed Dr. House he was right. Dr. House explained the only way to get rid of the stain was to grow new skin, which would take thirty days.