A blettod is a metabeing that has overpowered the mind of a person or animal such that it has total or near-total control over their body. It can also refer to an organism which has a blettod living in it or a metabeing that spends most of its time controlling animals. Only beings can become a blettod as the process is difficult to master.
General rules for blettods
1. The larger an organism is, the harder it is to control. Analogy: dog = car, human = helicopter
2. The more intelligent an organism is the harder it is to overpower.
3. Small organisms are too simple for metabeings to blettodise and not even worth trying most of the time. Their minds and bodies are too small to hold a metabeing capable of being a blettod.
4. Generally, blettods are indistinguishable physically from non-blettod organisms of the same species. However, a blettod can extend the lifetime of the animal it possesses by a (generally) small amount which increases for simpler and less intelligent organisms.
Considering these guidelines, blettods are usually mid-sized mammals as they offer the best trade-off between overall usefulness, lifespan, durability and ease of possession. Dogs and cats are the most popular targets, followed by pigs. Animals that come into contact regularly with humans are considered more useful.
Snakes are the traditional favorite because they're easy to control for their size (some might even say unnaturally receptive) and have the added bonus of creeping humans out. Blettod dogs tend to behave somewhat similarly to rabid dogs, partly because that's what scares people and partly because inexperienced blettods trying out a dog for the first time are likely to have poor coordination.
Blettods are usually solitary beings, but on rare occasion, they band together to possess beings that none of them would be able to overpower on their own. This tactic is almost exclusively used on humans.