At the 'Title' screen tap the candy on a string hanging out of the o in rope. If done correctly the candy will turn into an Easter egg. When you play the game the candy will be replaced by the egg and Omnom will wear bunny ears for a second when the candy goes close to him.
After the April 2011 update, you are able to tap candy on the string of the 'O' letter in rope on the title screen to make it turn into an Easter Egg. This will in turn cause candy in the game itself to be an easter egg, while Om Nom will wear a rabbit costume when he is tempted to eat!
Note: a more recent update now means you can tap the candy once to make it a donut, twice to make it a cupcake, and three times to go back to candy again.