Revealing mistake: When they are burying the Swede on the beach, you can see him blink when they throw sand into grave.
Revealing mistake: Take a good look at the crowd of backpackers waiting outside the office in which Richard just has been questioned by the police. They are the same people that later in the movie are welcoming Richard to their happy, secret paradise island community.
Chosen answer: In the alternate beginning, Richard is sitting in front of the large Buddha statue when a taxi driver stops and prompts him to take a ride with him. He explains that they celebrate New Year's by spraying each other with water guns, and gives one to Richard. While riding in the taxi, Richard sprays others and gets sprayed, having a lot of fun. It ends when Richard enters the "mall" where he will eventually meet the guy who offers him to drink the snake blood in the regular movie beginning. In the alternate ending, Sal turns the gun on herself and commits suicide. It ends by having a large ship rescue all of them when they're stranded at sea, banned from the island. The final words by Richard are something to the effect of "I have a lot of scars," which from what I recall is the actual ending of the novel by Alex Garland.