FarmVille: Free White Porcupine with Farm Cash purchase
Specifically, you'll see a large pop-up like the one below, offering you three choices for Farm Cash packages, but only for a limited time. You can purchase 4 Farm Cash for $1, 25 Farm Cash for $5 or 115 Farm Cash for $20 (presumably, you could purchase any of the packages and still receive the White Porcupine, but these are the only three packages listed). Honestly, these promotions are the best time to spend just a single dollar, as you may not end up with much Farm Cash, but you'll walk away with (normally) exclusive animals that would cost much more than a dollar if purchased in the store at normal price.
My own in-game ticker places this promotion at just one hour remaining, but your own game may differ slightly. Either way, make sure you login to your farm sooner, rather than later, to see if you can take advantage of this offer (and earn your free White Porcupine) before it's too late.
Will you purchase any of these Farm Cash packages to receive a free White Porcupine? Sound off in the comments.