ralph roberts , unaware that the hair his fingers were combing through had grown thicker , and that threads of black were visible in it for the first time in five years , jive-toured his apartment , walking on the balls of his feet , first humming and then singing an old rockand-roll tune from the early sixties : `` hey , pretty bay-bee , you ca n't sit down ... you got ta slop , bop , slip , slop , flip top alll about ...