It was stated that there was only one place (which is on the beach), on the Island, that a Mobile Signal could be obtained - yet, an earlier scene, when JP & Ruby are boarding the Helicopter, the Pilot can be seen using his Mobile.
In the opening scenes where Bethan catches a fish with a spear, when she lifts the fish from the water the spear has entered the fish beneath the mouth whereas the spear would have entered the fish from above.