Dr. Nuno Capaz:

It is exactly like driving under the influence of alcohol. I am 1.94 m tall. If I am asked to walk a straight line, I will probably not be able to do it even when totally sober. My feet are too far away from my brain. If a person is a gymnast, they could be completely drunk and would not fail that straight line test. That is why a breathalyser is used and the straight line test or the touching the nose exercise and things like that are no longer used.