Athletes' Feet   photograph by Walter Iooss Jr.   With a medal on the line, a gymnast hangs on by her toes; oh, how those golden slippers got around the track in the men's 400 meters; and race walkers put their best feet forward in the men's 20-kilometer event.   photograph by Walter Iooss Jr.     photograph by John Biever Next Photo SI Olympic Dailies Day: 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18