They bring a dog up to your car and if it barks or wags it tail they say it "alerted" to drugs and they can take your car apart.
That happened to my mother and I a couple of years ago the CA-AZ border. We were stopped at a “fruit check” and the DHS dude wanted our passports.
No problem, but then his co-worker said that the dog had alerted on mom’s car. Pretty neat trick, considering that it had never even had a cigarette smoked in it.
After half an hour of the dog going in and out of all 5 doors of the car, over the seats, up and down in the back with his handler saying “dirty, dirty, dirty” the whole time, they let us continue on our way.
We were quite impressed, I must say. /s