When Maj. Sophie Jean (Yeong-ae Lee) and her Swedish liaison walk across the infamous "bridge of no return," they make a reference to an axe murdering incident which took place on the morning of August 18, 1976, when a group of United Nations personnel attempted to trim the branches of a poplar tree in the DMZ that were obstructing the view from a U.N. guard post. North Korean soldiers attempted to block the operation then attacked the U.N. personnel with axes. Capt. Arthur G. Bonifas (honored as Major postmortem), Lieutenant Mark T. Barrett, and four Korean soldiers were killed, and as many US soldiers were wounded. Present day, the camp that houses JSA personnel is called "Camp Bonifas" in honor of Arthur Bonifas who was killed that day.
During the course of the movie when the South Korean soldiers salute their superiors they say (phonetically) 'TUN-GIL!' This is Korean for 'UNITE!' It is used in the South Korean military (mostly army) because - even though the North wishes to reunify under the Communist rule, while the South desires it under democratic rule - the hopes and goals on both sides are for reunification.
If you listen carefully during the scene when Maj. Jean and her liaison are walking over "the bridge of no return", you can hear loudspeakers broadcasting over the DMZ. These are known as "propaganda speakers" - the north and south both have use these devices to broadcast - 24 hours a day, 7 days a week, 365 day a year - propaganda against one another as to why listeners should unify under their specific rule of government.
At the beginning of the South Korean patrol scene, at 30:46, you can see what appears to be a mound of earth, which is actually a grave. Departed Koreans were buried sitting up and overlooking their favorite piece of land. These burial mounds were known by American GI's as "Happy Mounds".