The Torah in Parashat Ahareh-Mot (18:23) forbids a male from engaging in intercourse with an animal. The Sefer Ha’hinuch writes that the Torah forbids such an act because G-d wants all creatures to reproduce their own species, and not to mix with other species. For this reason, the Sefer Ha’hinuch adds, creatures produced through crossbreeding are incapable of reproducing. For example, a mule – the product of a horse and donkey – cannot reproduce, and fruits produced through grafting are likewise unable to reproduce. G-d arranged the natural world in such a way that products of crossbreeding are not blessed with the ability to reproduce because he wanted all the original species to mate only within the same species to reproduce that species. All the more so, the Sefer Ha’hinuch adds, G-d does not want the human being, the crown jewel of creation, to mix with the lower species by mating with animals. This prohibition forbids intercourse with both Behemot (domesticated animals) and Hayot (non-domesticated animals). Although the Torah mentions here only “Behema,” this prohibition applies to all creatures. This prohibition applies to an animal of any age, even an animal that has just been born. Both regular intercourse (“Ke’darkah”) and abnormal intercourse (“She’lo Ke’darkah”) are forbidden by force of this Biblical command. If a man willfully transgressed this prohibition and had intercourse with an animal, in the presence of witnesses who warned him in advance, then he is liable to Sekila (execution by stoning), and the animal is likewise put to death through Sekila. The Gemara explains that the animal is executed for two reasons. First, even though the animal quite obviously cannot be blamed for what happened, nevertheless, since it did, after all, cause a person to commit this grievous sinful act, it needs to be put to death. Secondly, allowing it to live would bring shame to the perpetrator, as people who see the animal would immediately be reminded of the repugnant act the sinner had committed. The Torah has great sensitivity even to sinners, and wishes to protect their honor, and thus even if someone commits this grave sin, for which he is put to death, nevertheless, he is protected from additional shame. The animal is put to death only if the one who performed the act is at least nine years old. Of course, the one who committed the act is not executed unless he is a Halachic adult (age thirteen or above). Nevertheless, the Sefer Ha’hinuch writes that even if the perpetrator is a minor, he should receive some punishment for this shameful act as part of his training to observe the Torah’s laws. If the perpetrator was younger than age nine, then the animal is not put to death. This prohibition applies in all times and in all places. As mentioned, one who intentionally violates this prohibition in the presence of witnesses is liable to Sekila. If no witnesses saw the violation, then he is liable to Karet. If one transgressed this prohibition unintentionally – meaning, he was not aware that the Torah forbids such an act – then he must bring a Hatat (sin-offering).