As soon as you see the tray with the water glass balanced on one side you slide your fingers out from the restraints, placing them quietly on the floor beside you.  You curl your fingers around the handle of the hammer, reassuring yourself that it is still there.  Your heart beats madly in your chest.  You try to calm yourself, certain that he has to be able to hear the maddening sound of your beating pulse.  He pauses for a moment and starts to bend down to place the tray on the floor.  Your heart sinks as your plan suddenly spins out of control.  If he slides the tray over then your chances of success drop dramatically.  You'll have alot more ground to cover before you have your chance to strike.  The element of surprise will be a 50/50 shot at best.  Do you attack now and surprise him or do you wait for the inevitable opportunity that you know will present itself eventually.