Which of the following is NOT a symptom of carbon monoxide poisoning?

Carbon monoxide poisoning presents a range of symptoms primarily related to its impact on the body's ability to transport oxygen. Symptoms such as fatigue, weakness, and heart palpitations are common as carbon monoxide binds to hemoglobin more effectively than oxygen, leading to reduced oxygen supply to tissues and organs.

Weakness in the knees can occur as a result of systemic weakness and fatigue, as the brain and muscles suffer from oxygen deprivation. Fatigue itself is a prevalent symptom due to the lack of oxygen, causing individuals to feel lethargic and weak. Heart palpitations may arise from the body's response to hypoxia, as it attempts to compensate for the reduced oxygen availability by increasing heart rate.

In contrast, an increased appetite is not associated with carbon monoxide poisoning. Instead, this symptom does not correlate with the physiological effects of decreased oxygen in the body. The body experiences stress and distress when exposed to carbon monoxide, which typically results in decreased appetite rather than an increase. Thus, the only choice that does not fit within the common symptomatology of carbon monoxide poisoning is the one associated with increased appetite.