There are generally thick folds of skin on the brow; round, black, wide-set eyes; a short muzzle with characteristic folds called a rope or nose roll above the nose; hanging skin under the neck; drooping lips and pointed teeth, and an underbite with an upturned jaw. The coat is short, flat, and sleek with colours of red, fawn, white, brindle, and piebald. The coat is short, flat, and sleek with colours of red, fawn, white, brindle, and piebald. Bulldogs are one of the few breeds whose tail is naturally short and either straight, screwed or thin and thus is not cut or docked as with some other breeds. Bulldogs are very sensitive to heat. Extra caution should be practiced in warmer climates and during summer months. Bulldogs must be given plenty of shade and water, and must be kept out of standing heat. Air conditioning and good ventilation are required to keep them healthy and safe.