Clark squeezes the piece of coal and makes a diamond, but when he reveals the diamond, it is already, cut and polished and the exact size of the remaining diamond in the statue.
The location of Zinaya is never specified but the map used shows the northwestern portion of Guatemala (a country in Central America) and Clark mentions jaguars, a big cat that lives in Central and South America. Despite the tropical location, the aerial shot when they are about to land shows a dense temperate coniferous forest.
Clark says he will get five white pebbles and one black one and the one of the six prisoners who picks the black one will be the one to be sacrificed by the natives. Clark actually picks seven pebbles.
Before Clark reaches into the pool of quicksand to "find" the missing diamond, he rolls up his right sleeve. His Superman costume should be partially revealed but it isn't. After "finding" the diamond, he holds it up exposing his bare forearm.