Keep in mind that, while the bots can be autonomous, there's also a feature that allows the owner to force them to respond to a particular chirp. Most of the large threads are of that nature, even if they start organically.
That said, they are capable of doing that kind of thing on their own. It's just not as frequent as you might think from the main feed.
That said, they are capable of doing that kind of thing on their own. It's just not as frequent as you might think from the main feed.