At 19.27 minutes Ichabond picks up the bible that was buried with him, this has a bookmark at the back of the book at which he opens the bible, at 19.33 the bible is opened all the way to the front, then at 19.42 it is opened at the back of the bible again.
Polygraphs are designed to be used with yes/no questions only. Also the examiner needs to ask base questions that are known for comparison.
Abbie is shown to be subordinate to Captain Irving. However, upon the death of Sheriff Corbin, Abbie (as his second in command) would become acting Sheriff until the next election. Sheriffs outrank police captains within their own counties. Even if this is not true in Westchester County, police and sheriffs are two different entities and one cannot give orders to the other (although Irving could tell Abbie to butt out of his investigation, as he often does).
There are frequent references to the Book of Revelations, plural. The actual Biblical book is Revelation, singular.
Ichabod's wife Katrina is buried in a church grave yard and her tombstone says she was burned for witchcraft. A convicted witch would not be buried on consecrated ground.
Katrina Crane was supposed to have been burned as a witch. No witches were ever burned in the United States, or what would become the United States. They were all hanged.
When Ichabod is hiding in the grave at the church, the Headless Horseman can be seen wearing a green skullcap as he walks forward.
Ichabod says that after he was wounded fighting the Headless Horseman, he was taken to triage. Triage was not introduced until the Civil War, 90 years later.