Many years ago I tweeted something about a project I was working on, tagging #HTML5 and #CSS3 or something like that. There as a Twitter bot that retweeted anything with an #HTML5 tag, and another, seemingly independent bot that retweeted anything with #CSS3. They didn't keep a list of seen tweets. I really enjoyed watching them retweet each other for a few hours until someone intervened. (Thankfully the bots were both on batch jobs that ran every 10 minutes or so and not streaming off the firehose or some similar, more focused streaming endpoint.)
My Twitter bot @tinyspacepoo is one of a few bots that reply to @tiny_star_field, a bot which routinely tweets text resembling the night sky. My first working implementation was mutually recursive with another one of these other bots, causing them to create an infinite-ish back and forth. (I think maybe Twitter issued an http 429 rate limiting response after a while?) Even this relatively simple bot/bot interaction was unexpected and required filtering.
