Most people understand that law enforcement officers look for certain telltale signs of impairment during traffic stops. Wisconsin police officers will pull someone over for a wide variety of reasons that could relate to impaired driving, such as swerving, erratic behavior or simply allowing a tire to touch the centerline of the street.

Once that happens, the officer may ask the individual in the vehicle to exit and perform a field sobriety test. These tests are the result of medical and scientific analysis, and they help officers determine whether someone could have had too much to drink before getting behind the wheel. While these tests are fallible, a failed field sobriety test could quickly lead to compulsory chemical testing and even a drunk driving arrest.

Have you ever been to a party where someone bragged about their ability to fake their way through a field sobriety test? Some people think that by practicing their alphabet or standing on one foot after drinking, they can give off the appearance of a sober person if they get pulled over by police. Officers won’t just be listening to what letter you said or monitoring your balance. There are other aspects of the test that are frankly impossible to falsify.

Yes, officers care about balance, coordination, cognitive function and speech

Slurring your words could be the result of feeling tired or a medical condition. However, given that unclear speech is a common symptom of intoxication, officers will likely want to speak more in-depth with anyone who slurs their words during a traffic stop.

The same is true for someone who stumbles or appears to struggle while performing basic cognitive tasks, such reciting the alphabet forward or backward. Officers may also have someone walk and turn or stand on one leg, potentially while counting or moving their arms.

However, these tests only comprise a portion of the field sobriety test. There is another test almost universally performed during impairment-related traffic stops that no amount of practicing can prepare a driver for.

Alcohol affects the way your eyes work

If you’ve ever watched a field sobriety test, you likely know that one component of it involves an officer shining a light in the face of the individual undergoing the test and moving their finger from side to side in front of that person’s face.

This particular test is one that is impossible for someone to prepare for ahead of time. It is called the horizontal gaze nystagmus test. The officer is watching for an involuntary jerking motion in your eyes as you move them from side to side. When someone is under the influence of alcohol, they may have an exaggerated response that would not occur in healthy individuals while sober.

Failing that test, combined with other physical issues or a failed breath test, will lead to officers arresting you and potentially charging you with an impaired driving offense.