(י) שמעו קול שאומר איש פלוני מת והלכו ולא מצאו שם אדם משיאין את אשתו ואם שמעו קול זה בשדה או בבור או בחורבה אין משיאין על פי אותו קול דחיישינן שמא שד הוא כיון שיצא הקול ממקום שהשדים מצויים שם:
(10) If they heard a voice saying "So-and-so died," and they went [to look] but did not find a man (i.e. they did not find a source for the voice), they may still permit his wife to remarry. If they heard this voice in the field or a cistern or a ruin, we do not permit remarriage on the basis of this voice because we are concerned that it came from a demon, as the voice derived from locales frequented by demons.

And there was another incident in Tzalmon, a city in the Galilee, where a particular man said: I am so-and-so, son of so-and-so. A snake bit me and I am dying. And they went and found his corpse but could not recognize him, yet they went ahead and allowed his wife to marry based on what he said in his dying moments. GEMARA: Rabba bar Shmuel said: It was taught in a baraita that Beit Shammai say: The judges of a court may not allow a woman to marry based on the statement of a disembodied voice; they require actual testimony. And Beit Hillel say: The judges may allow a woman to marry based on the statement of a disembodied voice. The Gemara asks: What is Rabba bar Shmuel teaching us here? This is simply our mishna, since the decisive ruling follows Beit Hillel’s opinion. The Gemara answers that he teaches us this: That if an anonymous mishna or baraita is found that states that the judges may not allow a woman to marry under such circumstances, it is simply the opinion of Beit Shammai, and is not the accepted ruling. With regard to the incident where they heard a disembodied voice but went and found no person there, which is mentioned in the mishna, the Gemara asks: Perhaps it was a demon. Rav Yehuda said that Rav said: They saw that he had the form of a person, so they knew it was not a demon. The Gemara asks: They, i.e., demons, also appear similar to people. The Gemara answers: They saw that he had a shadow. The Gemara asks: But they also have a shadow. The Gemara answers: It was a case where they saw that he had a shadow of a shadow. The Gemara asks: But perhaps they also have a shadow of a shadow? Rabbi Ḥanina said: Yonatan the demon expert said to me: They have a shadow, but they do not have a shadow of a shadow.
תניא אבא בנימין אומר אלמלי נתנה רשות לעין לראות אין כל בריה יכולה לעמוד מפני המזיקין
אמר אביי אינהו נפישי מינן וקיימי עלן כי כסלא לאוגיא
אמר רב הונא כל חד וחד מינן אלפא משמאליה ורבבתא מימיניה
אמר רבא האי דוחקא דהוי בכלה מנייהו הוי הני ברכי דשלהי מנייהו הני מאני דרבנן דבלו מחופיא דידהו הני כרעי דמנקפן מנייהו
האי מאן דבעי למידע להו לייתי קיטמא נהילא ונהדר אפורייה ובצפרא חזי כי כרעי דתרנגולא האי מאן דבעי למחזינהו ליתי שלייתא דשונרתא אוכמתא בת אוכמתא בוכרתא בת בוכרתא ולקליה בנורא ולשחקיה ולימלי עיניה מניה וחזי להו ולשדייה בגובתא דפרזלא ולחתמי' בגושפנקא דפרזלא דילמא גנבי מניה ולחתום פומיה כי היכי דלא ליתזק רב ביבי בר אביי עבד הכי חזא ואתזק בעו רבנן רחמי עליה ואתסי:
In another baraita it was taught that Abba Binyamin says: If the eye was given permission to see, no creature would be able to withstand the abundance and ubiquity of the demons and continue to live unaffected by them.
Similarly, Abaye said: They are more numerous than we are and they stand over us like mounds of earth surrounding a pit.
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).
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.
Middlemarch, George Eliot

