def create_followup(self, post, content, anonymous=False):
        """Create a follow-up on a post `post`.

        It seems like if the post has `<p>` tags, then it's treated as HTML,
        but is treated as text otherwise. You'll want to provide `content`
        accordingly.

        :type  post: dict|str|int
        :param post: Either the post dict returned by another API method, or
            the `cid` field of that post.
        :type  content: str
        :param content: The content of the followup.
        :type  anonymous: bool
        :param anonymous: Whether or not to post anonymously.
        :rtype: dict
        :returns: Dictionary with information about the created follow-up.
        """
        try:
            cid = post["id"]
        except KeyError:
            cid = post

        params = {
            "cid": cid,
            "type": "followup",

            # For followups, the content is actually put into the subject.
            "subject": content,
            "content": "",

            "anonymous": "yes" if anonymous else "no",
        }
        return self._rpc.content_create(params)