Yoreh Deah Siman 24 Seif 8

ח הֶחְלִיד אֶת הַסַכִּין תַּחַת הָעוֹר, אוֹ תַּחַת צֶמֶר מְסֻבָּךְ בְּצַוַּאר הַבְּהֵמָה, אוֹ תַּחַת מַטְלִית הַקָּשׁוּר בְּצַוָּארָהּ, אוֹ שֶׁהַמַּטְלִית מְדֻבָּק בּוֹ בְּשַׁעֲוָה וְשָׁחַט, (ו)שְׁחִיטָתוֹ פְּסוּלָה; אֲבָל אִם הַמַּטְלִית פָּרוּשׂ עַל צַוָּארָהּ וְשָׁחַט, שְׁחִיטָתוֹ כְּשֵׁרָה. וְיֵשׁ מִי שֶׁפּוֹסֵל גַּם בָּזֶה, וּלְכַתְּחִלָּה יֵשׁ לָחוּשׁ לִדְבָרָיו.

 

Seif 8

 

If one hides the knife under the hide or under tangled wool in the neck of cattle or under knotted cloth on the neck or cloth that is stuck with wax and slaughters, his slaughter in not acceptable. If however, the cloth is spread on the neck and he slaughters, his slaughter is kosher. There are those [that say] this is also not permitted. Ab initio, there is a concern in the matter. Accordingly one should take heed with sheep as they have tangled wool on their neck. One should tear or pluck the clinging wool so as not to do “chaladah”. (as if one inserted the knife between one sign and another.)