Which behavior may indicate a possible alcohol impairment during the HGN test?

The behavior indicating possible alcohol impairment during the HGN test is the inability to maintain gaze on a stationary object. When a person is impaired by alcohol, their ability to fixate their gaze can be affected. The HGN test assesses the smoothness of the eye movements as someone follows a stimulus (like a pen) horizontally. A person who is not impaired will be able to maintain their gaze steady and smoothly on the object. However, if someone struggles to keep their focus or has jerky movements while attempting to do so, it suggests a level of impairment likely due to alcohol consumption. This is an essential part of determining impairment during field sobriety tests, as intact tracking and focus are critical indicators of motor function that alcohol can diminish.