 Morgan has noted that the plot for " Roosters " , and the previous instalment " Owls " , grew out of the internecine conflict seen within the Millennium Group in " The Hand of St. Sebastian " , an earlier second season episode he had penned with Wong . Morgan had wanted to introduce secular elements to the series ' focus on eschatology , after the theological focus of the earlier episode ; he began focussing on ideas such as biological warfare as a possible way of depicting the end of the world — an idea which would later play out in the two @-@ part episodes concluding the second season , " The Time Is Now " and " The Fourth Horseman " . Millennium 's composer Mark Snow spoke positively about the series ' producers for their decision to use operatic music in this episode , rather than relying on " hip @-@ hop or rock and roll " as prior episodes had done . 
