This question relates to the first therapy session that McMurphy and the reader is witness to, which centres on the character of Harding and his supposed "problems." The reference to Harding being hurt comes after the session has ended, when the patients have ripped in to him as part of the therapy session and then are ashamed of their own viciousness. In theory, the Therapuetic Community is supposed to help individuals by discussing their weaknesses and issues, but the reality is shown through the way that McMurphy compares the Therapeutic Community to a group of chickens that pecks one of its members to death:
The flock gets sight of a spot of blood on some chicken and they all go to peckin' at it, see, till they rip the chicken to shreds, blood and bones and feathers.
McMurphy develops this analogy, saying that the chicken pecking carries on as all the chickens savagely peck at each other until they are all dead. This is the nature of Harding's wound, and it relates to the way that other patients, and Nurse Ratched, deliberately shame and humilate Harding and raise his problems and issues in a very insensitive and unhelpful way.