This actually refers to their singular method of catching their quarry, to the untrained eye ,they appear to "stumble ", over their prey,and inexperienced dog handlers have stated that they lack nose and only find game by accident.
Nothing could be further from the truth,properly brought on ,"in the right hands",these dogs exhibit a cunning remarkable for its deception, they have been filmed walking past sitting rabbits and clapped hares ,apparently unaware they are there.This is the sagacity and stumbling instinct showing itself,the quarry is lulled into a false sense of security,and before