Rav Huna said: Each and every one of us has a thousand demons to his left and ten thousand to his right. God protects man from these demons, as it says in the verse: “A thousand may fall at your side, and ten thousand at your right hand; they will not approach you” (Psalms 91:7).

The Gemara elaborates: With regard to one who relieves himself between a palm tree and a wall, we said that he places himself in danger only when there are not four cubits of space between the two objects. However, if there are four cubits, we have no problem with it. The demons have enough room to pass, and he will not obstruct them. And furthermore, even when there are not four cubits, we said there is a problem only when the demons have no other route besides that one. However, if they have another route, we have no problem with it.

The Sages taught: A person should not drink water from rivers or from ponds at night. And if he drank, his blood is upon his own head due to the danger. The Gemara explains: What is this danger? The danger of blindness. The Gemara asks: And if he is thirsty, what is his remedy? If there is another person with him, he should say to him: So-and-so, son of so-and-so, I thirst for water. And if there is no one else with him, he should say to himself: So-and-so, my mother said to me to beware of shavrirei, the demon of blindness. He should continue to say the following incantation, in the first part of which the demon’s name gradually disappears: Shavrirei berirei rirei yiri ri; I thirst for water in white earthenware cups. This is an incantation against those demons.

Summarizing the effects of the demons, Rava said:The crowding at the kalla, the gatherings for Torah study during Elul and Adar, is from the demons;
those knees that are fatigued even though one did not exert himself is from the demons;
those clothes of the Sages that wear out, despite the fact that they do not engage in physical labor, is from friction with the demons;
those feet that are in pain is from the demons.

One who seeks to know that the demons exist should place fine ashes around his bed, and in the morning the demons’ footprints appear like chickens’ footprints, in the ash. One who seeks to see them should take the afterbirth of a firstborn female black cat, born to a firstborn female black cat, burn it in the fire, grind it and place it in his eyes, and he will see them. He must then place the ashes in an iron tube sealed with an iron seal [gushpanka] lest the demons steal it from him, and then seal the opening so he will not be harmed. Rav Beivai bar Abaye performed this procedure, saw the demons, and was harmed. The Sages prayed for mercy on his behalf and he was healed.