Salaah becomes invalid for example, if a person laughs loudly while praying Salaah, or if he hurts his body and thereby draws out blood, if he forces himself to pass wind, or if a person walks on the roof and by walking there a stone or anything else falls down on the head of a Musalli (praying Salaah) and he starts to bleed – in all these cases the Salaah will become invalid. This is because all these actions are carried out through the will of man.