Other mistake: As the murderer spots a police car coming towards him he turns to his right onto a dirt road, there is a huge boulder at the point where he turns, marked "No trespassing, Bishop Falls camping". As he turns he sideswipes it, rocking the boulder, however the sideswipe has no effect on his vehicle.
Other mistake: When Lea Jansen and Dave Ryder want to leave the room, which is called the "deep freeze", they hear Kalgon and his men coming and "hide" next to the door. When Kalgon and his men enter, the movie wants to tell us that they cannot see Lea and Ryder, although they are obviously in their field of view.
Other mistake: The two headed monster's heads are pretty big. Big enough to swallow a person whole. But when Val Kilmer jumps on one to impale it, the sword comes out of the bottom of the monster's head. For this to happen, the sword would have to be unbelievably large, larger than a man, which he would be unable to wield anyway.
Other mistake: The Duke is picked up in New York. They are headed to L.A. via Chicago. Jack has Eddie wire $500 to Amarillo, Texas. The route from Chicago to L.A. would not take them anywhere near Texas.
Other mistake: When Rico has Walter in the jungle, he yells to Dundee "I know you're up there" (and it echos), then he yells "come down" (and it echos), then he says "or I will shoot your friend", but that line doesn't echo.
Other mistake: Christina suggests that they have found Atlantis. However, they start in Hawaii, which is in the Pacific. The general consensus is the Atlantis is in the Atlantic (or Mediterranean) and not the Pacific. Some people do suggest that the lost continent of Mu is in the Pacific.