FarmVille developer Zynga has another hit on its hands with FrontierVille, a pioneering sim that's picked up an amazing 16.3 monthly active users in just a few weeks, making it the fastest growing app on Facebook for some time now.

Looking to reward its players, the social game developer unveiled the Manure Collection, a new set of virtual items that players could gather over the holiday weekend -- finding them all unlocked the saltpeter item, which users needed to create fireworks.

The Manure Collection included a variety of alliterative animal crap -- Poultry Puddin', Piggy Poop, Brush Brownie, Prairie Pile, and Meadow Muffin -- produced by virtual sheep, horses, goats, and other creatures in FrontierVille.

GameLife, which discovered and pointed out the collection, notes that virtual goods have now reached their "poop-stained nadir".