Instructions
Open the "Angry Birds" application on your device and scroll to world number five, called "Ham 'Em High." Tap once on the world's icon to open it.
Go to level 13-12 and tap on its icon once to open the level. Note that "Angry Birds" levels must be completed in sequence, at least until all levels are unlocked. You have to successfully complete all of the levels preceding 13-12 before it will be available for play.
Shoot the first bird, a yellow one, anywhere.
Shoot the second bird, a white one, backwards by slinging the slingshot to the right instead of to the left and releasing. When the bird is over the backside of the hill that holds the birds, tap anywhere on the screen to release the bird's egg. Hit the hill about halfway down to the ground and the golden football will appear in the middle of your screen.
Go back to the "Angry Birds" main menu and navigate to the "Golden Eggs" world to play the bonus level associated with the golden football.