No explanation is ever given for how the very British speaking Ben (Oliver Reed) has come to have such an 'Americanised' family. Even in the childhood flashback scene illustrating Ben's fear of undertakers, he is seen attending an outdoor American funeral.
Car trouble: when Ben (Oliver Reed) and his son try to flee from the evil house in the family station wagon, we see how Ben forcefully bashes the car into a large fallen tree numerous times. Yet just a few scenes later, the car shows not a nick or dent anywhere on the body. It's obvious that in their isolated location, no body or repair work could have been performed on the car to put it back into such pristine condition.
At the end of film the mansion-house chimney is seen to become unstable, collapsing and ultimately falling on top of David - he is killed. During this time however the chimney breaks up so slowly that the observant child would have had enough time to get out of the way of such a dangerous hazard.
When escaping from the renewing house with his son, why does Ben relentlessly plow his automobile into a fallen tree? Surely, it would have made more sense to drive an alternate escape route; or even abandon the car altogether and escape on foot.
There is no clue or significance in the movie of the prop antiquated bicycle found in the woods, or the Edwardian/Victorian spectacles found in the pool. It is never actually specified, for instance, that they have any relationship to the 1890s graves. Indeed Ben's (Oliver Reed's) sudden bout of madness upon discovering the cursed glasses in the pool, could have played identical, with or without the spectacles.
There is no explanation for what has happened to Marion (Karen Black) when the movie ends. She does not appear in photos of the other family members 'absorbed' by the house. While the elderly reclusive 'Mrs Allardyce', whom Marion has supposedly become, does not in fact exist.
Ben's shock dramatic jump from the small upstairs bedroom window at the end of the movie - confirmed by Dan Curtis on the Burnt Offerings commentary - is both out of character and beyond reason. Ben has not shown any suicidal tendencies, and, while his distress is acceptable, he would still not have reacted in such a strange and extreme manner to his wife's erratic behavior (which in any case has been obvious throughout the film). The scene exists purely for dramatic effect.
It is inexplicable that there is never any police investigation and arrest, given that dozens of people have vanished when visiting the country mansion (Dunsmuir House). The Rolf family, for instance, having recently attended Aunt Elizabeth's funeral, must have sent out invitations or made phone calls from the mansion informing relations, shortly before they too disappeared. The doctor was also aware that the Rolfs had leased the mansion. Leading the authorities to suspect the Allardyce siblings and Walker of foul play.
At the end of the movie Ben (Oliver Reed) dives from the upstairs bedroom window on a vertical descent, but inexplicably lands horizontal on the station wagon beneath, his face smashing into the windscreen in one continuous drop.
Ben (Oliver Reed) is seen chopping bushes in the garden midway through Burnt Offerings. When he pauses for a rest, he suffers a terrifying waking nightmare as a black hearse drives up the road to the house, pauses, and the phantom chauffeur smiles at him insidiously. The delusion then ceases abruptly! Yet, although the black hearse is supposed to be unreal it leaves a small oil leak on the concrete path where it was previously parked, after it has vanished.