For the source text click/tap here: Yoma 41
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The Mishna on our daf describes how the lashon shel zehorit was placed on the two animals. In the Gemara, Rav Dimi quotes Rabbi Yohanan as teaching that there were two other occasions where a lashon shel zehorit was used, in the case of a metzorah (someone suffering from Biblical leprosy), where it was used as part of the purification process (see Vayikra 14:4), and in the case of a parah adumah (the red heifer) where it was used as one of the ingredients for making ashes that would be used in the purification process (see Bamidbar 19:6).
In both of those cases, the Biblical sheni tola'at is identified with the lashon shel zehorit. This lashon shel zehorit (literally "a tongue [strip] of crimson") was a bundle of combed wool that was rolled into the shape of a tongue and dyed red (carmine) with a crimson pigment derived from cochineal insect. These insects are found infesting various types of wood, and its blood is the source of this dye.