Why was Michael Phelps sporting big red circular marks on his body?
The simple answer is that he - like many other Olympians in Rio - is a fan of "cupping" - an ancient Chinese healing practice.
Practitioners of the healing technique place specialised, round circular cups on the skin. Then they use either heat or an air pump to create suction between the cup and the skin, pulling the skin slightly up and away from the underlying muscles.
The suction typically lasts only for a few minutes, but it can cause the capillaries just beneath the surface to rupture, creating the circular, photogenic bruises that have been so visible on Phelps.
Physiologically, cupping is thought to draw blood to the affected area, reducing soreness and speeding healing of overworked muscles.
But there is not much science to determine whether it offers a real physiological benefit or whether the athletes simply are enjoying a placebo effect - a tiny moment of releasing the pressure of all that expectation and tension.
The byword in sport these days is "marginal gains" - tiny, incremental adjustments in kit, technique and training that, when added together, make for big improvements.
Think of cupping as the anti-science version.
After all, most athletes have their own rituals and superstitions - and if a lifetime of dreaming of gold came down to a few minutes of your life, you would take every edge you can get too, and feel all the better for it.
THE GUARDIAN, NEW YORK TIMES