Further, we can now explain the widespread custom of covering up mirrors or turning them to the wall after a death has taken place in the house. It is feared that the soul, projected out of the person in the shape of his reflection in the mirror, may be carried off by the ghost of the departed, which is commonly supposed to linger about the house till the burial. The custom is thus exactly parallel to the Aru custom of not sleeping in a house after a death for fear that the soul, projected out of the body in a dream, may meet the ghost and be carried off by it. The reason why sick people should not see themselves in a mirror, and why the mirror in a sick-room is therefore covered up, is also plain; in time of sickness, when the soul might take flight so easily, it is particularly dangerous to project it out of the body by means of the reflection in a mirror. The rule is therefore precisely parallel to the rule observed by some peoples of not allowing sick people to sleep; for in sleep the soul is projected out of the body, and there is always a risk that it may not return.

Sir James George Frazer