Well, so much for the patient being the mutant.
Panel 1: We see John singing "Country Roads" off-key to a patient who I initally believed to be a boy of roughly 10 years of age sitting in the chair with the nitrous mask over his (or her) face.
Panel 2: Said patient is confused for a second as John adjusts the flow of the gas. Perhaps it's less because he stopped singing and more because the words "Adjust! Adjust!" are floating in mid-air. After all, if s/he starts seeing sound effects, s/he may be getting too much anesthetic.
Panel 3: In any event, John resumes signing horribly as he starts working on the patient's mouth.
Panel 4: He then tells Jean that he believes if a patient can stand his singing voice, he or she is adequately sedated.
Hypothesis: I do believe we'll have a wrap-up to this tomorrow. Also, the patient is a young girl in her early teens.