Laying an egg is an ability you can unlock for your chicken form late in the game.
In Infierno, after defeating Zope and Cactuardo, go back to the shaft where the group of workers wouldn't let you through before. Continue through it and up. At the top, go the right and there will be a chicken dungeon. Complete the dungeon and unlock this ability.
Once you've unlocked it, press
12 times and this achievement will unlock.