Audio/visual unsynchronized: When Al is playing the piano he is clearly not pressing any of the keys, just moving his fingers across the tops of them.
Revealing mistakes: In the first shots of Al hitchhiking, the film is reversed. The cars are driving on the wrong side of the highway and the drivers sitting behind the wheel are sitting on the right side of their vehicles.
Errors in geography: When Al is asked by Joe, the truck driver, in the Reno diner about his plans, Al says he is headed east. Joe tells him is driving north to Salt Lake City. Salt Lake is east of Reno.
Revealing mistakes: After Al strangles Vera, a shot of Vera hanging off the bed clearly shows her long eye lashes fluttering.
Crew or equipment visible: When Al Roberts is dragging Charles Haskell Jr's body from the car into the bushes on the side of the road, you can see the rain-making apparatus shooting water up into the air to generate the rain.