The Egyptians believe that the soul (Ba) takes the form of a bird with a man's head, and that it leaves the body at death and flies to the gods. They believed that the soul would return to the mummy regularly to offer it comfort and reassurance of its immortality. It is sometimes depicted as flying down the shaft of a tomb to the mummy, or perched on the mummy's breast. It is often portrayed holding the ankh. 'The Book of the Dead' promises plenty of food to the Ba, so its conception is not purely spiritual.