If no two snowflakes are identical, as we’re taught as little kids, it’s a no-brainer that the same must hold true for people. This extraordinarily simple yet remarkable film from David Ostry proves that theory by concentrating on, yes, legs. Not like in the ZZ Top song of the same name, mind you, with its music video vixens flashing impossibly perfect gams that stretched from here to Cleveland. No, this “Legs” features only the lower extremities of mere mortals, shot from the upper thigh on down to the toes. Exquisitely cut like a music video to a catchy Alan Parsons-ish instrumental from the group “Massive Attack,” this film depicts an astonishing number — and an even more astonishing variety — of human legs. Now, legs are pretty much taken for granted, aside from the occasional glance at a particularly blessed man or woman wearing shorts. Not here, however. Posing in various positions, alone or in groups, standing still or active, bare-footed or shoe-clad, this thing is all legs, all the time…and the effect is absolutely mesmerizing. If nothing else an editing tour-de-force by Ostry, “Legs” is pure fun; an amazing film essay that’s guaranteed to bring a goofy grin to your face, even as it slowly becomes surreal and obtuse before your very eyes.