the russian courier-riders outside the pavilion had of course heard all the proceedings ; laurence saw one young enthusiast , as angry as alexander himself at the indignity offered the tsar , jerk deliberately upon the chain of his dragon 's bridle , and jab it with a spur , so the dragon snarling lashed its head forward to pull the rein loose , placing its jaws directly in napoleon 's path scarce half-afoot from his head .