When Shannon and Charlotte emerge from the ocean, Shannon's chest is completely smooth. For the remainder of the film, which is supposed to take place that same day and the day after, copious amounts of chest hair can be seen at the opening of his shirt.
The Church schedules Morning Prayer and Holy Communion as a single early service, with "Sermon" as a separate service later. In 1964 the Episcopal Church used the 1928 Prayer Book, which had Morning Prayer as one service and Holy Communion as another service. A sermon wouldn't be a stand-alone event, either service could include one.
Contrary to the opinion of some, in the opening shot of the church, a torrential rainstorm does not take place under a cloudless sky, it's a solid overcast sky -- hard to differentiate on black and white film.