Which of the following is NOT one of the four clues observed during the HGN test?

The correct choice identifies "Rapid eye movement" as not one of the four clues observed during the Horizontal Gaze Nystagmus (HGN) test. The HGN test is a standardized field sobriety test used to detect signs of impairment, particularly from alcohol consumption. The four specific clues that officers look for during this test are:

1. Lack of smooth pursuit, which refers to the inability of a subject's eyes to follow a moving object smoothly.

2. The onset of nystagmus prior to 45 degrees, indicating involuntary jerking of the eyes that begins before reaching the standard lateral gaze angle.

3. Distinct and sustained nystagmus at maximum deviation, which assesses how well the eyes maintain their position when looking to the side.

"Rapid eye movement" is not a recognized clue in this context. The resulting behavior observed during the HGN is categorized specifically as nystagmus, which involves the eyes moving in a jerky manner rather than rapidly. Thus, the answer effectively points out that this terminology does not align with the established categories used in the HGN assessment.