Wudu is a fixed sequence — hands, mouth, nose, face, forearms, head, ears, feet — performed before prayer and repeated whenever it is broken by sleep, using the bathroom, or bleeding. The rules include a dry alternative (tayammum, with clean earth) when water is unavailable or harmful, which is characteristic of the law's practicality. Muslims describe the effect as a threshold marker more than a cleaning: the sequence is short enough to be automatic and deliberate enough to change gear.