Cutting the brake line of a vehicle and thereby causing a high speed crash as shown with the Land Rover is a common TV trope. The problem is that this assumes 1) the driver will not step on the brake pedal before the high-speed crash (if they did so beforehand, such as when leaving their driveway, they would notice the problem and avoid the crash), 2) the driver will not downshift or turn off the engine (called engine braking which will slow and stop a vehicle), and 3) that when they do step on the pedal the only option will be to hit a fixed object such as a tree. In fact, here the vehicle could have been easily steered to one side of the tree.
Barnaby's DVD of Cy Davenport's movie fast-forwards like a video cassette. The lines that show on the screen would not show on a DVD.
When Barnaby discovers Colin Yule's "mummified" body, the actor's eyelids can be seen to move behind the bandages.
When Davenport is murdered, he first falls on to the banisters with a knife in his back. As he does, the knife wobbles as if it were made of rubber, or at least not made of metal. Then, as he falls, it's clear he's rotating to fall onto his back, as the stuntman would always prefer when landing on a padded mat or airbag. But the body lands on its front side.
A bald man wearing jeans is just visible around the 1:19:47 mark to the right of the screen behind Emma and Diana when they enter the crypt.
Barnaby and his wife are seen at the film viewing as the film is just starting. At the same time, the ambulance and police are across the way at the crime scene. The first issue here is they do not hear the sirens from the emergency vehicles. Next, Jones arrives and by the time Barnaby gets the call on his mobile the film is over. Since most films run well over an hour, it would not take that long for Barnaby to be called to the scene.
At the autopsy, the doctor gives the cause of death, pronouncing the victim had no medical problems. The body is seen laying on the table with the scalp intact. One of the first things done in an autopsy is to pull the scalp back and cut the skull open so the brain can be weighed and examined. While the statement made could cover the internal organs, it could not rule out something like a brain tumor or embolism, which given the circumstances would only be detected by an examination.