When , after weeks and weeks of cautious driving of scattered elephants across the hills , the forty or fifty wild monsters were driven into the last stockade , and the big drop gate , made of tree trunks lashed together , jarred down behind them , Kala Nag , at the word of command , would go into that flaring , trumpeting pandemonium -LRB- generally at night , when the flicker of the torches made it difficult to judge distances -RRB- , and , picking out the biggest and wildest tusker of the mob , would hammer him and hustle him into quiet while the men on the backs of the other elephants roped and tied the smaller ones .