During the HGN test, what tool does the officer typically use as a stimulus?

During the Horizontal Gaze Nystagmus (HGN) test, the officer typically uses a pen or finger as a stimulus. This choice is correct because the officer needs a clear, focused object that the subject can follow with their eyes. A pen or finger is ideal because it can be held steady and moved smoothly, allowing for a precise assessment of the subject's eye movement and any signs of nystagmus.

Using a pen or finger allows for the best execution of the test, as it helps to elicit the involuntary eye movements that are characteristic of impairment from alcohol or other substances. This assessment involves observing the way the eyes move as the officer ensures that the stimulus is moved in a systematic manner from side to side. The other options, such as a flashlight, small mirror, or piece of paper, do not provide the same level of control or effectiveness for this specific test.