An Austin, Texas was arrested for driving while intoxicated, even though he had no alcohol or drugs in his system. The man was originally stopped for running a stop sign. The officer had him do the field sobriety tests, which they claim he failed. They also had him blow into a portable breathalzyer, which showed no alcohol. Not to be deterred, they too him to jail.
At the jail he was asked to blow into a breathalyzer, and registered 0.00. You would think that would be enough, but it wasn't; they still booked him into jail, and charged him with DWI. He provided a blood sample, which was sent off for analysis. The blood test confirmed the breathalyzer - he had no alcohol or drugs in his system.
So what does this tell you? I think several things. For one, you can get arrested even when you're not intoxicated. It also shows how unreliable the field sobriety tests are; they really are agility tests, which some people can never pass. Finally, it shows how hard it is for a police officer to change his mind once he's formed an opinion.
Fortunately, it worked out for this gentelmen. However, he still had to go to jail, pay for a bond, and hire a lawyer. Not someone anyone wants to do.