I was on an aeroplane last week. A man sat next to me with a dog on his lap. I asked him about the dog and he replied that it was a sniffer dog.
So the dog went off up the aisle, it soon returned and put one paw on the man's lap. The man said that meant somebody had heroin on the plane.
Off went the dog again and returned and put two paws on the man's lap.
The man said that meant someone had cocaine on the plane.
Off the dog went again, this time it returned and jumped onto the man's lap and immediately pooed. When I asked what that meant he said the dog had found a bomb.