Trivia: A video game from Sega in 1972 was called Killer Shark, considered the first video game in the horror genre. The object of the game was to shoot at a giant shark with harpoons. This game can be seen in the seaside arcade in the movie.
Trivia: Often touted as the first "summer movie;" what this refers to is the now-typical marketing practice of doing most of the advertising before the film's release to build up hype ahead of a big nationwide opening weekend (at the time most movies opened in a limited number of markets to build a reputation). By the 80s this model was followed by big tentpole "summer blockbusters," but nowadays is the norm for the majority of studio releases year-round.
Answer: Possibly a scar from having his appendix removed, I've been told.
The appendix shot is Brody - he is feeling inferior as the other two share tales of the sea and the only scar he has is from his appendix being removed.