Sanhedrin 54 - Why is the Animal Also Stoned?
The law is that the animal with whom bestiality was committed is also stoned . What is the reason for this strange law? If the person sinned, in what way did the animal sin? - Since the downfall came upon a man through it, it is also stoned, so that others should not come to sin through it as well. Another explanations: so that it should not occur that an animal passes in the street and people say, "This is the one that caused So-and-so to be stoned."
But how do we know that the punishment is indeed stoning? This is derived from the use of the same words, "You shall surely kill him", concerning this man and concerning one who instigates others to idolatry, about whom it says " You shall pelt him with stones ."
Art: Jacopo BASSANO - Sheep and Lamb