According to the Mishna on today’s daf, one of the biblical prohibitions that would lead to the punishment of sekilah – death by stoning – is bestiality. Thus, sexual relations by a man or a woman with an animal is forbidden by the Torah, and such an act is punishable by death – for both the person and the animal that was involved (see 20:15-16 “And if a man lie with a beast, he shall surely be put to death; and ye shall slay the beast. And if a woman approach unto any beast, and lie down thereto, thou shalt kill the woman, and the beast: they shall surely be put to death; their blood shall be upon them.”).
The Mishna raises an obvious question: Since it is clear that in such a case the instigator of this sexual interaction is the man or the woman we can certainly understand why the Torah requires them to be punished – but why should the animal be punished, as well? Two answers are offered in the Mishna. One possibility raised is that this animal served as a “stumbling block” before the person, which is reason enough to kill it. Another suggestion is that we do not want the animal to be a center of interest, whereby people would see it in the marketplace and comment “that is the animal that led to so-and-so’s being stoned.”
The Tiferet Yisrael explains these two suggestions as follows. According to the first reason, given that the animal has already served as a “stumbling block” to one person, we are concerned lest another person may choose to sin with it, as well. According to the second reason, even though the person has committed an act that is punishable by death, nevertheless the Torah concerns itself with the person’s honor.