McDonalds Burgers: Why don't they mold - EVER? We eat this.

http://www.therealfoodchannel.com/videos/food-insanity-1/still-eating-fast-food-burgers.html

There are some OLD Burgers but they NEVER get mold on them?  We eat this stuff.  What are the secret ingredients.  Are they healthy?  Probably not.