Myths of the Norsemen: From the Eddas and Sagas

It was generally believed among the Northern nations that the soul escaped from the body in the shape of a mouse, which crept out of a corpse’s mouth and ran away, and it was also said to creep in and out of the mouths of people in a trance. While the soul was absent, no effort or remedy could recall the patient to life; but as soon as it had come back animation returned.