h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

When mowing a lawn, it is generally a good idea to wear on the feet something that covers the entire foot. Sandals are not a good idea. If sandals are worn, a phenomenon known as Green Toe can result. This effect will last until a shower is taken and the toe thoroughly washed (with soap, mind you). In the meantime, it can be an effective prank to walk around with bare feet, exclaiming that you have one of the following diseases: leprousy, gangrene, or if the green is dark enough, the bubonic plague.