In-N-Out’s secret menu has to be the worst-kept secret ever. They even have a separate page for it on their official website. Numerous websites tell about even more available options (more search results). I even just found a photo on Flickr that’s apparently of an official container for Animal Fries:

In-N-Out Animal Fries by “Atwater”on flickr

Of course earlier today I ordered an animal style cheeseburger well done with the bun extra toasty and the spread on the side. If I didn’t feel like I had already bugged them enough with my pickiness I would’ve customized the burger further.

UPDATE (February 1, 2010): An expanded secret menu has now been posted on In-N-Out’s Facebook page.