Invisible

The human body is such a fragile, imperfect construct... A little cut or a strong hit to a weak point, and all its functions break down... But that's not what makes it the most faulty. It's our senses. Take the human eye, for example. It is only capable of registering a finite amount of snapshots in a second, just like our brain isn't capable of processing any more of them. Of course, that's enough for us most of the time; no human can move faster than what they themselves can see. However, others might not have the same limits we do... Was that slight blur, that almost-subconscious sense of motion caught from the corner of your eyes a figment of your imagination? I would double-check.