I think my very favorite thing in Rian Johnson's "Looper" is a squiggly cloud. It hangs there in the sky above a cornfield and you can't help but notice it. Which is good, because this is a time-travel movie and the cloud comes in handy later when something happens again in this same spot and the cloud tells you what time it is. Thanks to that cloud, you know this is a re-run.
In one version of the present-future-past, Joe (Joseph Gordon-Levitt) shoots his future self (Bruce Willis) and in another he doesn't. I couldn't remember why that happened at first just now, but then it came back to me. Johnson brought in Shane Carruth, writer-director of the meticulously planned and way more convoluted time-travel thriller "Primer" (2004) to do some special effects work, which indicates to me that RJ is fairly serious about his science-fiction. (He also wrote and directed "Brick" and "The Brothers Bloom," both of which contain some nifty, well-plotted twists.)
(Update: Here's a "Looper" timeline/infographic.)