"Ahu" are stone platforms on which many moai sit. There are 313 known ahu and 125 of these carry moai. The biggest, Ahu Tongariki is 220 m (720 ft), and had the most (15) and tallest moai.
With 'Good Will Hunting,' Miramax made certain the recruited audience wasn't expecting to laugh at Robin Williams like they normally do. From my limited experience, you can really blow test screenings by conducting them in the wrong way.