At one point at the Skinner home, Morgan and Brian put their rifles away in a wooden crate on the jeep, but when they get to where the rats are, they pull the rifles directly out of the vehicle.
At the end, in a long shot, Lorna the female scientist steps off the cabin porch towards the pile of dead rats and completely unscrews the lid from the jar of F.O.T.G. to dump it over the rats. In the subsequent close shot, the lid is securely back on and she unscrews and removes it again.
When the ferry delivers the two friends back, the same cars; a Ford LTD Wagon, a Chevy Vega and a Pontiac LeMans also drive off the ferry. On the very next ferry ride, the same cars are show on the ferry and departing again.
In an early scene with Morgan, Davis and Brian on horseback chasing a deer, the second rider's horse nicks the top of a fence rail, bringing one end down to the ground. However that rail isn't there when the third rider's horse jumped the fence to take another rail down.
After Mr. Skinner is killed by the rats, you can see his closed eye fluttering as the rats carry him off.
When Morgan first meets Mrs. Skinner's rooster, the legs (from the knees down) are visible of the crew member wielding the giant chicken head.