Beating is the most common form of physical torture. When the aim is to disguise its effects, beating may be performed with heavy, flexible implements such as sandbags or lead-filled plastic pipes, which may leave short-lived bruising but no permanent scarring. Sometimes the torturers perform the beating over clothing or folded towels. The impact of the blows is still severe and such beating may cause deep muscle bruising (which may take several days to reach the surface) or internal bleeding. This has been reported to lead to acute renal failure due to release of myoglobin (see Module 5). In many countries, severe beatings, which cause widespread bruising, are discontinued after the first few days of detention so that when the victim is produced to court or released after days or weeks later, all obvious signs of beating will have faded.