Final answer:
Without additional context about the exchange between Colonel Harrison and Gerry, it's impossible to determine the reason for the joke or Gerry's response.
Step-by-step explanation:
The student's question pertains to the motive behind a character named Colonel Harrison's joke and another character, Gerry's, response to it. From the provided excerpts, it appears that the interaction being referenced isn't directly included. Therefore, based on the information given, it is impossible to determine the specific reason for Colonel Harrison's joke or Gerry's precise response. Both provided texts refer to different emotions and reactions not specifically linked to a joke made by Colonel Harrison or Gerry's direct response to it. Thus, without additional context or reference to the specific joke and response in question, the scenario falls beyond the scope of the given information, and a definitive answer cannot be provided.