Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is based on the 1937 Agatha Christie novel with the same title and it takes place that same year. It's part of her series of novels with the French detective Hercule Poirot played here by the director Kenneth Branagh who also starred in and directed Murder On The Orient Express in 2017 which is also based on one of Christie's novels. Death on the Nile was also made into a movie in 1978 which has a completely different snake scene than this movie. (As far as I know, the novel does not have a snake scene in it.)
Poirot is known for having a very large mustache. Branagh supersized it in Murder on the Orient Express with a thick creation that wrapped halfway around his face and was punctuated by a soul patch. I must not have been the only person who wondered why it was so ridiculous because this movie starts with a long war scene that is only included as a back story about the mustache which we learn Poirot grew to cover up a large facial wound he received from an explosion during the first world war. Thanks for not letting us make fun of a wounded war hero again, Branagh, but I don't know if it's worth the scar shaming message.
The main story involves a wealthy young heiress Linnet Ridgeway (Gal Godot) who marries Simon (Armie Hammer). We see them celebrating in a luxury hotel on the banks of the Nile River in Egypt. Poirot is there as the guest of a mutual friend. Simon's former fiance Jacqueline (Emma Mackey) shows up to spoil the party.
The Snake Scene
The next day we see Linnet and Simon at an outdoor market in some ruins. Then we see Poirot talking to a woman snake charmer. He asks her if her snake is her friend and she tells him it is her best friend. (I like snakes, but that is a bit extreme even to me.) Simon and Linnet walk downstairs and talk to Poirot, apologizing for last night's drama. Suddenly the snake leaves its basket and races up to Linnet, striking at her. Poirot quickly stops the snake with his cane before it can bite her. Linnet is shocked and thanks Poirot. The snake charmer apologizes and grabs the snake. Then Linnet and Simon ask Poirot to help them get rid of Jacqueline who has been stalking them on their honeymoon.
The snake scene is a foreshadowing of the dangers in store for Linnet, along with the brick that nearly kills her, and it also gives Poirot a chance to be a hero, showing how cool and capable he is in a dangerous situation, and how fast he is with his odd cane. Unlike the falling brick, which was pushed by someone, the snake incident could be an accident, but it could also be that someone paid the snake charmer to open the basket and send the snake to attack Linnet. If it's an accident, then it's just another ridiculous example of a snake attacking a person in a movie for no reason other than to let the hero prove himself. If the attack was intentional, then it's another ridiculous example of trying to use a snake as a weapon because there's no way the snake charmer would be able to know that the snake would only attack Linnet and not someone else then return to its basket.
It would make more sense plot-wise if the snake was trying to kill Poirot, which is what happened in the 1978 movie when a cobra was left in his cabin. The person who wants to murder Linnet would benefit if the master detective was not around to solve the crime. But I can't find any way to interpret the scene that way. Linnet thanks him which shows that she felt she was the target. The snake charmer apologizes, but she would do that in either case, so that doesn't proove anything. And by the way, there is no snake in the novel this movie was based on. To me that means it's just another example of a snake used to make a foreign land more exotic. In the same way, they also tossed in a shot of a CGI crocodile to make the CGI Nile River background look more authentic.
The snake is a dual-fanged movie cliche CGI monstrosity. I don't like it, but I understand why everybody uses CGI snakes these days - it's safer than dealing with a live snake; an animated snake can be made to act any way you want which a live snake won't do; and it avoids all accusations of exploitation or animal abuse, especially when a snake is killed.
More Snake Trivia
We were told that Linnet played Shakespeare's Cleopatra on stage, and later we even see her standing on a ladder dressed as a giant Cleopatra for fun, complete with a nice snake headdress. Seeing that I couldn't forget that Cleopatra died from snake bite. After the snake charmer incident newlyweds Linnet and Simon walk out onto a precarious ledge when they are visiting some monumental ruins. They start groping each other as she starts quoting lines from the play Cleopatra. As she speaks the line "Where is my serpent of old Nile?" a huge brick falls from above and nearly kills her.