Plus random messages send to different users. Something like enforced SPAM that is marked as SPAM inside the encrypted message. Your Client can decrypt the messages and discard the SPAM automatically. Sometimes the client can even reply to such a SPAM message automatically.
THis makes it easier to hide with WHO, HOW OFTEN and HOW MUCH you are communicating.
I'm not sure that the SPAM messages are necessary. I don't think that you can do traffic analysis of this sort on Tor without compromising the local machine (you want to monitor) or something like >15% of the Tor routing network.
