Decades ago when I was still enlisted I was in my barracks room on a day off. It was around noon and I was making a ham and cheese sandwich at my desk.
Law Enforcement came through the barracks with the drug dog and it went nuts at my door. The cop encouraged the dog to enter and it came over to me. The cop tried to get the dog to sniff around and give the "alert" again but it had smelled the ham and placed his head on my leg and begged me for a bite.
I guess that would be a false positive.
Not from the dog's point of view.
Well, see, it all fits! Because conventional wisdom tells us that any DA worth his salt could get a grand jury to indict that ham sammich.