1: In the end , when all of them are leaving the island, you see a shot of them under the helecopter.

2: You can see that the blades of the helecopter are spinning fast enough that they can take off an instant later, yet when all of them were under the helecopter, their hair was sitting flat on their heads, evidence that Spielburg used a bluescreen but for got to use wind effect on the actors. =)