After Austin, Texas, police pulled Larry Davis over for running a red light, they asked him to take a breathalyzer test. He agreed, knowing he hadn't had anything to drink. Sure enough, he blew 0. In fact, he even came up clean on a blood test that looks not only for alcohol but for seven types of drugs. The cops still arrested him for DWI. Prosecutors ultimately threw out his case. In fact, local prosecutors say they throw out about 30 percent of DWI cases because the Austin police have so little evidence.