Pet Society, Playfish's popular pet simulation game on Facebook, turns two this week (on August 8 to be exact). Basically, Pet Society launched before Facebook gaming became a 'thing,' so it's refreshing to see that one of our favorite social games seems to have some longevity. But, I digress.

In honor of the big birthday, Pet Society's weekly update includes a slew of party-themed items, which includes two new collaborative items: the Party Invitation and the Surprise Birthday Box.

The party invitation requires six materials (1 Balloon, 2 Paper and 3 Markers) that you can get from friends or by purchasing them with Playfish Cash. Once you have completed the invite, you can place it a room in your pet's house and then select three friends to come and enjoy the celebration with you. Only one party is available per room, and the party will last all week.



The Surprise Birthday Box also requires friends to build -- 15 friends in fact. To request help, click the 'Ask' button and post a message on your Facebook wall. Friends who help will get coins as a reward.



Once the Birthday Box is built, well, I'm not sure what's inside yet -- but if you know, leave a note in the comments below.