This is maybe the most fascinating phenomenon I came across while looking for stuff for this thread - do click and play with it!!

"Biological Motion" - it demonstrates how the brain and visual system can form a 'Gestalt' just from some moving dots:

BioMotionLab

One very compelling example of the visual system's ability to recover object information from sparse input is the phenomenon known as biological motion. Here the activity and identity of an animate creature are compellingly created using just a dozen or so "light points" strategically placed on the individual's body (Johansson 1973). With these animation sequences, no single dot conveys information about the object or event being depicted - individual dots merely undergo translational and/or elliptical motions. Perception of a biological organism engaged in an activity must entail global integration of these motion signals over space and time - perception of such animation sequences is literally the creation of motion information (in the same sense that perception of an object in a random-dot stereogram is the creation of binocular disparity information). When viewing point-light displays, observers can identify the gender of an actor (eg, Kozlowski & Cutting 1977; Mather & Murdoch 1994), the activity in which he/she is engaged (Johansson 1973) and, even, the emotional state of the actor (eg, Brownlow et al 1997). Human infants as young as 3 months of age can perceive biological motion (eg, Fox & McDaniel 1982), as can non-human mammals (Blake 1993).