In the modern age, most judicial systems recognise that animals cannot be held responsible for "crimes" because they lack the cognitive ability, and the moral agency, to tell right from wrong. But this wasn't always the case.
In the Middle Ages, animals were routinely subjected to the same criminal charges, and proceedings, as humans. In fact, criminal trials against animals were considered perfectly normal, and were conducted right up into the 18th century. The podcast Criminal covered one such case from the 1400s, in their very first episode. This rather famous animal trial featured a pig, who was tried for the murder and mutilation of an infant. The pig was found guilty, and sentenced to death by hanging.
Pigs were common defendants in medieval animal trials, mainly due to different way in which livestock were kept at the time. When we think of farm animals, we think of large herds contained by acres of a fencing, but in the Middle Ages, the number of animals being farmed were much smaller. Most peasant families owned one or two animals - a pig, a couple of chickens and maybe a goat or a cow for milking - and these animals were largely free roaming.
More often than not, the victims of animal "homicide" were children, because the living conditions of the time bought them into close, regular contact with livestock. Medieval children, unless they were members of the aristocracy, were not educated, so they were not in school during the day. They were put to work from the moment they were of an age and size to do so, usually in the same fields as their parents. When not working, they were playing in the muddy streets, right alongside all the roaming farm animals. Deaths due to frightened or enraged animals encountering small children were fairly common, especially as what would be considered a minor injury today, would be life-threatening in medieval times. In a society where hygiene is non-existant and antibiotics haven't been discovered yet, an open wound, however small, can be a death sentence.
But trying animals for the death or injury of humans wasn't the only type of animal trial, there were also the religious trials. The Middle Ages were an era of Biblical literalism, and of witch trials, where the Roman Catholic Church was systematically stamping out "the competition" - paganism, midwifery, herbalists and other traditional forms of folk medicine. Part of that campaign included demonising certain animals, as the demonic familiars of witches. Black cats are the most obvious candidate, but they were by no means the only targets of the astute witch hunter. Cats of any colour were fair game, as were dogs, certain types of birds, rats, and insects.
One particular case, recorded by the infamous Witch-finder General, Matthew Hopkins, is that of Jane Wallis of Huntingdonshire, East Anglia. According to Hopkins, Jane Wallis had two familiars who went by the names Grizzel and Greediguts. In her confession (obtained by torture, of course), Wallis claimed that the familiars could take almost any form, but appeared most often as greyhounds with a bristle of hog hair running down their backs. She also confessed to suckling these creatures from her "Witch's marks." These marks, also called Witch's teats, were believed to be a permanent mark that the Devil placed upon the body of an initiate witch, as a visible sign of her compact with the malignant forces. These marks were most often described as being wart-like in appearance, the origin of the modern caricature of the witch with the wart on her nose that we see in popular culture.
In reality, these witch's teats were actually real warts, scars or birthmarks, marks that the person who possessed them had no control over, but were enough to condemn them.
Another common type of animal trial, while less likely to end in the cruel and unnecessary death of an innocent creature, is every bit as disturbing as the other examples I've discussed in this post. In fact, it's a little bit more disturbing on some levels. These are trials for beastiality, which was apparently a lot more common than I am remotely comfortable even thinking about. The reason I say that these trials where less likely to end with the execution of the animal is because, in many of these cases, the animals were recognised as the "victims" of men with unnatural urges.
In case you weren't disturbed enough already, I'd just like to point out that it appears that animals had more rights over their bodies than most women at this stage in history. God, that's depressing.
But, back to the unnatural urges. Defendants in these trials usually tried to claim that the animal had "seduced them" in some way, but, according to historical records, it seems judges generally rejected these claims on the basis that animals weren't capable of consent, nor of seducing anybody. The accused beast-lovers were usually put to death, and the animals given a reprieve, probably on the grounds that killing them was a waste, because nobody wanted to eat sausages made from the pig that Billy Bob had his dick in last week.
By the 1800s, animal trials were nowhere near as common as they had been in the Middle Ages, but they still occurred from time to time, and there are even a few well-known examples of animal trials from the early 20th century. The most notable being a circus elephant which was put on trial, and hanged, for killing it's trainer. In fact, while researching this subject, I even found a case from 2008. That's right, a 21st Century animal trial...sort of. The trial occurred in Macedonia, where a wild bear was accused of stealing honey from a local beekeeper's hives. The bear was found guilty, but since no-one wanted to even attempt to extract damages from a wild bear, the park's service was given a hefty fine instead.
I think this is where I'm supposed to make some kind of bad joke about pic-a-nic baskets or something.