How does Nurse Ratcheds reaction to McMurphys singing and to his boxer shorts develop her character?

The confrontation between Nurse Ratched and McMurphy has clear sexual undertones. Indeed, one of the major themes of the novel involves the contrast between liberated and repressed sexuality. By appearing in front of Nurse Ratched wearing only a towel—and threatening to lose even that—McMurphy confronts her with the prospect of forbidden nakedness. In their final major confrontation, it will be Ratched whose nakedness is exposed against all propriety and at the hands of McMurphy. The fact that McMurphy is actually wearing boxer shorts reveals that he is playing a game with Ratched and figures correctly that she is vulnerable to his charms or at least to his threats of startling activity. Significantly, this is the first moment at which Nurse Ratched shows any strain or tension. McMurphy thus begins to find a place for a wedge and make Big Nurse crack, in line with the bet that he made with other patients.