If you want to discover the tweets between users, this service called Snap Bird is an option. It’s totally free and is in English but is quite easy to see and filter the messages we want.
Twitter is difficult to follow the messages between one another tweets. This service allows you to filter those messages. Only you have to allow entry application to login with your Twitter account and go!
Also, you can filter tweets that you mention, direct messages, favorites of someone on Twitter, and much more. The service makes a first analysis in a given period of time, but it is possible to be extended.