Cara runs a very interesting mail art project called "The anthropomorphic mailart project". You can see the details on her blog (http://chewytulip.blogspot.fr/). The idea is that she sends you a rubber stampped image of the head of an animal and you send her back a postcard integrating this head in a mail art. I contacted her and she sent me back the following envelope and items, together with two stamped animal heads. I will show you soon what I did using one of them.