In the Roman Empire someone who killed their parent would be sewn into a sack with a live rooster, dog, monkey, and snake, and then thrown into the water. In medieval Germany, they used a cat, a dog, and a picture of a snake.
Killing one’s parents was a grave sin, and the Roman Empire had a rather exotic punishment for those found guilty of this heinous crime. First, the murderer was whipped and their head covered with a bag (either made of leather or a wolf’s hide, for some reason). Then, they were stuffed into a large sack made of leather from an ox. Into the sack went a bunch of live animals, such as a dog, a monkey, a rooster, and a viper. And then the whole thing went into a river or the ocean. Because the sack was relatively watertight, the murderer and the animals probably suffocated before they could drown.
I cannot find a good explanation for why this particular ritual, or why this particular combination of animals. It seems like something dreamed up to make the execution as cruel and excruciating as possible, along the same lines as being thrown to wild animals or crucifixion.
The practice carried over into the Byzantine Empire, then died out around the end of the 9th century CE. It was resurrected in medieval Germany – the Holy Roman Empire – without the rooster and with a cat replacing the monkey (I imagine monkeys were considerably harder to find in the Holy Roman Empire than in the Roman Empire). If they were short of snakes they could substitute a picture of a snake instead – following the symbolism of the punishment if not the reality, I guess. The last recorded instance of the poena cullei, the penalty of the sack, was as late as 1749.