Revealing mistake: When the stegosaurus begin to move around a lot, you can see the one that is charging at her steps in the creek water, but there is no splash or any ripples.
Revealing mistake: When Sarah is making her way to the baby Stego, just before she gets on her belly and crawls closer to it, you can see the kneepads she has on.
Revealing mistake: In the beginning of the movie, when the rescue group arrived on Isla Sorna, the actress grabs the Nikon F5 of the photographer and makes her way to the nest of the Stegosaurus. After several shots of the small Stegosaurus there is no more film left in the cassette, so the camera begins to rewind it automatically. The thing is, you never see the rewind knob moving although you hear the camera's motor rewinding (The Nikon F5 has a manual rewind knob to be able to rewind the film when the batteries are dead). There was obviously no film at all in the camera.
Revealing mistake: When Kelly does her acrobatics and kicks the raptor out through the window it is possible to see that the raptor is pulled through the window as it "flies" upward and scrapes against the top of the window frame and then straight down. As the raptor falls down 2 wires can be seen reflecting light outside of the window, one even falls down after the raptor.
Revealing mistake: When the T-rex escapes into San Diego, it enters someone's backyard to drink from their pool. When the Rex plunges its face into the water, the water barely ripples and its bottom jaw is as clear as day below the surface of the water. If a beast of that size were to dip its head in the water, no matter how gently, it would've created a ripple that would distort the surface of the water quite significantly.
Revealing mistake: When the dinosaurs are released from their cages and are running around the camp, a jeep is launched into the air and lands almost on top of the 2 hunters who leap from the tree. When the jeep falls forward, and down out of the tree the bottom of the tree moves and shakes in a way it shouldn't if it was truly made of wood.