Which symptom may indicate the presence of pain?

Dilated pupils can indicate the presence of pain due to the body's physiological response to stress or discomfort. When a person experiences pain, the sympathetic nervous system is activated, which can lead to the release of stress hormones like adrenaline. This activation can cause the pupils to dilate as part of the fight-or-flight response, allowing more light to enter the eyes and enhancing visual acuity. This physiological change can be an important indicator in clinical assessments to help recognize pain in patients.

In contrast, other options do not typically suggest the presence of pain. Decreased heart rate and decreased respiratory rate are more commonly associated with relaxation or deeper states of health rather than pain. A calm demeanor suggests a lack of distress, which would generally not be expected in someone experiencing significant pain. Therefore, dilated pupils serve as a key symptom to consider in the assessment of pain.