Corrected entry: Maxim tells his wife that he carried Rebecca's dead body to the boat from the dinghy and he carried her below to the cabin floor. It is hard enough to get yourself out of a dinghy and onto the "sailboat" (as it is known) and then down the narrow stairs to the cabin. Carrying a bag of groceries only adds to the problem. But a dead woman - impossible.
Corrected entry: In the scene where Max de Winter brings Mrs. de Winter to Manderley for the first time, we see Frith, the butler, at the estate gates. A few minutes later, after the de Winters have finished driving down their mile-long driveway, we see him at the front door of the mansion. How'd he make it back there so fast?
Correction: The man welcoming the DeWinters at the gates is another staff member Max greets, calling him Smith, it is not Frith.
Correction: This is speculation at best, some people might not have a problem carrying groceries down narrow stairs and many people (like firemen) are trained, strong enough, or just determined, to carry a body. Nothing about his statement is impossible.
Bishop73