for ever after , he would see how postumus and quintus started moving in from the sides of the room , passing behind the vipienas , how at first it seemed they were coming towards him to help with the wine , and then he realised where they were headed , and he was too far away to do anything ; how in a single movement their hands went down to their belts , and up again with steel flashing , and across , and down , and they stepped away as they sheathed their knives .