Corrected entry: When the kids are dancing near the fire, you can see that their wooden spears are not sharpened on either side. But when they kill Simon they are sharpened somehow.
Corrected entry: This is also in the original Golding novel - Piggy is nearsighted, which is corrected with negative (diverging) lenses. A positive (converging) lens is necessary to focus sunlight. However, the boys use his glasses to make fire, but they would not work.
Corrected entry: When the other boys drop the rock on Piggy if you watch in slow motion you can see that the rock collapses and springs back
Corrected entry: When Simon is floating in the water after being murdered, you can (barely) see him swim away. Pretty impressive, considering that he is dead!
Corrected entry: Piggy's glasses get broken, and he starts crying about them, but later on he's wearing his glasses again which some how get fixed.
Corrected entry: In one scene, when Piggy and Ralph go for a walk, Piggy suggests to build a sundial because there is no watch left after the accident. Later, after Simon's death, you can see Piggy with a watch around his left wrist.