In Castlevania: Harmony of Despair for the Xbox 360, there is a hidden item in each chapter that will boost your end score when you collect them.
The Moai is hidden in Chapter 3. Fall through the center of the vortex in the background from the top of the stage to make it appear.
There are six hidden items to collect, so check out my guide to find the other hidden items in Castlevania: Harmony of Despair.