According to the Rabbis, a man should not drink water by night, for thus
he exposes himself to the power of Shavriri, the demon of blindness.
What then should he do if he is thirsty? If there be another man with
him, let him rouse him up and say, "I am thirsty;" but if he be alone,
let him tap upon the lid of the jug (to make the demon fancy there's
some one with him), and addressing himself by his own name and the name
of his mother, let him say, "Thy mother has bid thee beware of Shavriri,
vriri, riri, iri, ri," in a white cup. Rashi says by this incantation
the demon gradually contracts and vanishes as the sounds of the word
THE TALMUD, _Avodah Zarah_, fol. 12, col. 2.