Femto, to put it simply, is the instantaneous. A period of time so short that normal living beings can't even imagine it. Time is made of constant instants so short that you can't perceive them. Since you can't perceive the instantaneous, time appears to be continuous, but it's actually made up of tiny instants. Those ropes also appear to be single pieces of rope, but in reality they're woven together from much smaller threads. And so, these ropes woven from imperceptibly thin fibres seem like an infinitely continuous material. We remove all unwanted materials to make them the strongest fabric possible. That includes, of course, any unwanted impurity. By weaving those threads together into ropes, you can make a rope that will never rot. Since time immemorial, we've used these ropes to restrict the movements of the impure.