In reality none of these threads matter because Grime has told us that the dogs are not 100% reliable...so just how reliable are they..nobody really knows
I don't see how any claim of 100% accuracy can be proved. If a dog was sent into a field to search - and didn't alert then the handler would assume there was nothing there to alert to. However without digging up the whole field - what he cannot know is whether there was something there- and the dog had simply missed it.
I'm impressed by all sniffer dogs, but IMO one of the main reasons why false alerts can happen is when the dog is affected by the beliefs of the handler. i.e. unconscious cueing. This has been proved to happen in tests, and Grime acknowledges that it is a reason for false alerts.
Unless Grime and his dogs had been subjected to such testing - then he cannot possibly know for certain whether this could apply in his own case - as the very fact that such cueing is unconscious means that he wouldn't know he was doing it in the first place.
Anyone who has a dog will know they can pick up on the slightest, tiniest changes in body language.