Put Nadal on a wet clay court with Djokovic or even Gulbis, Roger Federer, or Tomas Berdych and he could suffer.

WSJ: Roland Garros: Return of the French Resistance

When rolled across wet clay, the image would appear in relief, repeated more than once if the cylinder was rolled over any length.

WSJ: The Ur-Metropolis | Uruk | Pergamon Museum | By A.J. Goldmann

Observations from orbit have identified clay and sulfate minerals in the lower layers, indicating a wet history.

ENGADGET: NASA's Curiosity rover receives long-distance OTA update, 'brain transplant' on Mars