as @RaceProUK said, not much.
here’s the implementation with the relevant parts highlighted.
https://github.com/AccaliaDeElementia/SockBot/blob/master/sock_modules/emoji.js#L121-L135
Basically it follows /posts.json, looking for posts owned by the user the bot is operating on, that haven’t been touched by the bot before. then does a find/replace on a set of emoji, adds a hidden footer and fires off an edit post.