Theory #2 - The younger woman is a paid assassin, hired to kill someone at precisely 5:48. Through careful practice and training, the assassin knows that it will take her exactly three minutes to reach her position, assemble her sniper rifle, and liquidate her target. So, she needs to finish picking out a dress before then. Ironically, her target-to-be is the very woman that is helping her with her dress purchase. This is funny.
Theory #3 - The woman trying on dresses is a stripper, working at a nearby gentleman's' club, and her shift begins at 5pm. Despite the fact that her profession involves taking off her clothes, she seems preoccupied with buying the right dress. This is apparently funny.
Theory #1 - The explorer's mother had a long and illustrious career - more so than her son. The natives know of his famous mother's fame. This is funny.
Theory #2 - The natives are worshipers of Cheeksa, the Polynesian goddess of buttocks, and they are performing her salute to the explorer who seems to have The Divine Ass-print on his chest, indicating that he is favored by Cheeksa. This is funny.
Theory #3 - I didn't know that the expression "saved our bacon" existed in 1965. This is funny.
Theory #4 - The natives believe that the explorer must be their mother, and since they live in a matriarchal society, they prostrate themselves before him. Unexpectedly, the natives living in a remote jungle village can read English, This is funny.
Theory #5 comes to us from Jim D. Thanks, J. Dee! - The natives are one of the Lost Tribes of Israel, therefore ANYONE'S bacon would be safe in their presence! FUNNY!!!!!!
[Commenter theories will be added to the post. -Mgmt.]