Which of the following is an example of a subjective observation?

A subjective observation is based on a person's feelings, perceptions, or opinions rather than measurable or observable facts. In this case, noticing that a patient is less talkative than usual reflects an interpretation of the patient's behavior rather than an objective measurement. The observation is subjective because it involves personal interpretation about the patient's communication level and does not rely on quantifiable results.

The other examples involve objective observations, which can be quantified or measured. For instance, finding that a patient has a fever is objective because it can be verified with a thermometer. Hearing a patient cough and noticing a rash are also objective observations because they involve direct, measurable signs of the patient's health condition. Therefore, the correct choice illustrates the key distinction between subjective and objective observations in the context of patient monitoring in healthcare.