Egg

(Yes, that's it)

To access the hidden modes, press and hold in either the upper-left, upper-right or lower-left corner for 1 second
Upper-Left: "Find The Invisible Egg"
-Drag your finger around on the screen
-Listen closely for audio cues to locate the hidden egg

Upper-Right: "Egg Piano"
-Press the keys to play a note
-Become a musician

Lower-Left: Egg Skins
-20 different skins
-Select a skin you like at no cost at all