3,101. Shaatnez

Hilchos Kilayim 9:11

An animal that was consecrated and then disqualified is treated by the Torah as if it has two bodies, even though it obviously doesn’t; it’s treated like a consecrated animal and a secular animal all in one. The animal is therefore like a non-kosher animal and a kosher animal mixed together, about which Leviticus 27:11 says, “If any unclean animal that may not be brought as a offering….” Our oral tradition explains that this refers to animals that were consecrated and then disqualified. Accordingly, if someone plows with an ox that was consecrated and disqualified, or if he mates such an ox, he is liable to the penalty of lashes for violating the prohibition of mixed species. This prohibition was transmitted via tradition.

Hilchos Kilayim 10:1

The prohibition of mixed fabrics in garments only applies to wool and linen as per Deuteronomy 22:11, “You shall not wear shaatnez, wool and linen together.” In seaside towns you’ll find something like wool that grows on stones in the Dead Sea (sic.; he's actually referring to the Mediterranean). It’s called kalach, it resembles gold and is very soft. One may not combine kalach with linen because it resembles sheeps’ wool and therefore resembles shaatnez. Similarly, one may not combine silk and kalach because it gives the appearance of wrongdoing.