Although the hearing was a coroner's inquest, which doesn't have the same rules of procedure as a court hearing, the swearing in of witnesses was inconsistently handled. Wald had to be sworn in before testifying, but Mrs. Saban was not sworn in before testifying about the parrot. And the criminologist also was not sworn in.
In their conversation on the park bench, Ellen Monteith tells Perry that two weeks earlier she had spent her honeymoon in the murder cabin, arriving on September 11 and leaving on Saturday, September 16. But September 16 was a Tuesday in 1958. It was a Saturday in 1956.
When Ellen Monteith reads the prop newspaper about the murder, one can see that the insides pages of the newspaper are blank.
The prop library book Perry observes at the cabin contains a misspelled word on the check-out form page where the librarians stamp the Borrowed and Due. The word is misspelled "Barrowed" at the top of two columns.