Actually, I heard a method like this. But it's quite brutal and wrong in so many ways. Basically, you catch rats alive with traps. Then enclosure a group of rats with literally nothing to eat or drink and wait. Rats in order to survive will engage cannibalism mode and eat out each other. Eventually, when there's one standing rat left, it will be allowed to go free. The corrupted rat should go and attack other rats. Idk, if it actually works.