Why do skunks smell so bad?

Skunks have two scent glands beside the anus that produce an oily spray rich in thiols, sulphur-containing chemicals whose odour humans can detect at extremely low concentrations. A skunk can aim the spray accurately at a threat about 3 metres away. Before spraying, skunks give warnings such as stamping their feet, hissing and raising the tail; spotted skunks even do a handstand. Spraying uses up a limited supply, which can take over a week to replenish, so skunks prefer to bluff. Their bold black-and-white colouring is a warning signal that predators learn to avoid.