Not to slaughter an animal in the presence of another

Question

I remember learning that you should not shecht an animal in a way, that another live animal will see it.

Is there a source to this?

Related: Are there any requirements in Kashrut about how livestock must be treated/reared during its life before reaching the slaughterhouse?

Answer 1

I also thought it was an explicit law but, after looking into it, it is less direct than that. I found a Pitchei Tshuva that brings down what you remember

It all starts with a gemara in Chulin 55b

The mishna states: Or if its lung shriveled [ḥaruta] by the hand of Heaven, the animal is kosher. The Sages taught in a baraita: Which is a ḥaruta? It is any animal whose lung shriveled. If this occurred by the hand of Heaven, e.g., if the lung shriveled from fright of thunder and lightning, the animal is kosher. But if it happened by the hands of a person who frightened it, e.g., if it witnessed another animal being slaughtered, it is a tereifa.

The SA in YD 36:14 brings this as halacha

צמקה כולה אם מחמת בני אדם שהפחידוה כגון ששחטו אחרת לפניה וכיוצא בזה טריפה

on which the Pitchei Tshuva comments

עיין בתשובת בית אפרים חיו"ד סי' כ"ו שכתב שלא נכון מה שהרבה בני אדם באים אל השוחט ואוחזים עופות בידיהם ועומדים סביב בכדי שמיד שיגמור שחיטת עופות של זה יתחיל בשלו ובפרט בערב יו"כ בשחיטת הכפרות ואין זה נכון כי יש בזה משום צער ב"ח וגם יש חשש צימוק הריאה ואף שאין להחמיר להצריך בדיקה מ"מ לכתחלה יש ליזהר בין בעופות בין בבהמות.

He writes (in the name of the Beit Efraim) that it is not right when people line up with chickens in their hands and surround the shochet to have him slaughter one after the other, especially during kaparot of Yom Kippur, as it is "tsar balei chaim" and there is also a suspicion of shriveled lungs. He writes that lchatchila one should refrain from having chicken and larger animals witness the shechita of other animals.

Answer 2

I suspect you may be thinking of Hilchot Sh’chitah 8:9, where Rambam rules that if an animal becomes physically frightened because it sees another animal being slaughtered, it (the frightened one) is treif.