Specify a tweet replying to a person, using URL
(like "http://twitter.com/someone/status/123456789") or
ID number(like "123456789").
You will get a set of tweets with the tweet you specified and
its target of reply, being chained repeatedly if the targeted tweets
replied to persons.
First, bookmark the link above. You will get the result of TwitterChain by only clicking the bookmarklet with opening a tweet page.