When Ellen drives back home from the Post Office, she parks her car in front of the gate in the fence along her driveway and goes inside. When Dr. Grahame drives up just a few moments later, Ellen's car is no longer in the driveway.
When Ellen reminisces about the time when she first met her husband George, she remembers her time at the beach with George and Doctor Grahame. While she is sitting on the beach drying her hair between the two men, she places her towel loosely across her lap. In the next shot with George and herself only, the towel has disappeared.
Needless to say, a two-page letter, mailed in a standard #10 business envelope, with no additional enclosure-- which appears to be all that the doctor burns, in a tabletop ashtray-- would not exceed the one-ounce limit for a standard first-class letter.
Ellen tells "Hoppy" that she won't have any cookies until after the grocery delivery comes. When the box of groceries arrives Ellen carries them into the house and begins putting them away. Hoppy comes in and Ellen goes to the cabinet on the opposite end of the counter and gets a box of cookies for Hoppy. But she never took a box of cookies out of the grocery delivery box and put them in the cabinet.
In his discussion with Ellen when she tries to retrieve the letter, Mr. Carston contradicts himself first by saying that he shouldn't give the letter back to her as she giving it to him was as good as putting it in a post box, then second by saying that he can't give it back to her as the letter writer is George i.e. someone other than her. If there is a policy of he not being able to return the letter to begin with (even though he was going to), the second policy would not exist.