tracking instrument” and the handler was regarded as reporting the movements of the instrument, in the same way that a constable in traffic case might have reported on the behaviour of his speedometer. It was argued in that case that the tracker dog's evidence could be likened to the type of evidence accepted from scientific experts describing chemical reactions, blood tests and the actions of bacilli. The comparison does not, however, appear to be sound because the behaviour of chemicals, blood corpuscles and bacilli contains no element of conscious volition or deliberate choice. But dogs are intelligent animals with many thought processes similar to the thought processes of human beings and wherever you have thought processes there is always the risk of error, deception and even self-deception. For these reasons we are of the opinion that in the present state of scientific knowledge evidence of dog tracking, even if admissible, is not ordinarily of much weight. ”