My dad, who is retired now, has a great story because of this. Before he retired, he worked at a metal producing plant and started getting "randomly" selected each month to get tested. After the 4th "random" selection he started keeping a poppy seed bagle in his desk. Sure enough, he got selected a 5th time so he immediately ate the bagle then went to get tested. 30 minutes later, he got sent home. Got 3 days paid vacation for a false positive because of state drug laws. He stopped getting "randomly" selected after that.