Revealing mistake: When the three boys are sitting by the fire the footage is repeated. At first the fire is normal, but suddenly the flames starts going downwards. (00:34:50)
Continuity mistake: When Ralph is running from the hunters at the end and he finds the pig's head on the stick, he stops with his arms spread out a bit. In the next shot, even though you only see his head and shoulders, you can tell that his arms are now straight at his sides.
Continuity mistake: After Jack places the pig's blood on Roger's cheek, he then places it on his own. Look at the amount of blood on Jack's index finger. It goes from a little to a lot.
Continuity mistake: After the rock hits Piggy on the head and he dies, from one angle his eyes are closed but from another angle they're open.
Continuity mistake: When Piggy is killed, in one shot there's only a bit of blood on his head, but in the very next shot it's all over his face.
Revealing mistake: When the boys use the glasses to start the fire, there is smoke coming from under the wood they are lighting. This wouldn't happen. It would come only from the focused point of light made by the glasses.
