Instead of following one another the sounds overlap; a sound which is acoustically perceived as coming after another one can be articulated simultaneously with the latter or even in part before it.
“Unlike some of the time-travel movies I love, like 'Primer' or '12 Monkeys,' 'Looper' is not about time travel. It's about this situation that time travel creates and the people dealing with that situation. So narratively, the big challenge was to have time travel get out of the way.”