One of the sages, Rav Huna the son of Torta, testified that he once went to a place where they mated animals to each other and there he saw a snake twisted around a turtle and wrapped around it, mating with it. After a while they had an offspring, the arod, a dangerous snake which bites humans and kills them. When he related what he had seen in front of R’ Shimon the Righteous, the latter responded: Just as people try to make changes to nature — mate animals even if they are not of the same species and create new mixed-breed animals, so does G-d, measure for measure, create a new animal (a dangerous snake) from the snake and the turtle. The scholars asked: How is it possible that the turtle and the snake should mate and be able to procreate? The sages already ruled that two conditions must be met for animals of different species to be cross-fertile. The first condition is that their mating positions are the same, such as the female behind and the male in front or the couple facing each other, as humans mate. The second condition is that the length of gestation is identical. The snake and the turtle meet neither of these conditions. Answer: It was a divine miracle which created this dangerous snake to punish the transgressors.
(Babylonian Talmud, Tractate Chulin 127a)