Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is an Agatha Christie murder mystery about a group of people, the kind who wear gowns and tuxedos to dinner, sailing on a sightseeing boat on the Nile River. A woman is murdered, then two others, and everybody is suspected until the great Belgian detective Hercule Poirot, who just happens to be on board, solves the mystery. It's like Murder on the Orient Express but on a boat. Much of the film is filmed on location in Egypt, the costumes won an Oscar, and it's great fun to watch the cast full of Oscar-winning actors chew up the scenery, but it's a bit draggy. Fortunately, there is a nice long scene with a Cobra used as a weapon to wake you up.
Peter Ustinov is detective Poirot. David Niven is Colonel Race, an ex-military man. They return separately to their adjoining cabins to freshen up before lunch. For Poirot, that means waxing his famous moustache. As he does this, we see a large cobra at his feet on the floor. Then he sees it and he freezes. Slowly Poirot moves his hand towards the wall separating his and Race's bathrooms and taps an SOS. Colonel Race hears it and runs to grab his cane, which has a sword in it, because who doesn't travel with a cane with a sword in it?! Race runs next door and slowly creeps up on the cobra, then stabs it in the throat with the sword and digs in. We see an extended shot of him twisting the sword around, just to make sure its dead, and then a shot of the snake falling to the floor. The dead snake looks different from the live one, but I doubt anybody noticed.
Poirot says to Race: "I must thank you for a most timely deliverance."
Race: "It's my pleasure. I heard your SOS. Do you think it was put there deliberately?"
Poirot: "Of course it was. But it will take more than a serpent to interrupt the investigation of Hercule Poirot."
The boat's manager enters the room and Poirot asks him to remove the cobra. He says he has never seen such a reptile in a first class cabin, then walks to the railing of the ship and throws the dead snake overboard.
Later after Poirot exposes the murderer, we learn that the snake was brought on the ship originally to kill someone else, but the plan was abandoned and the snake was then used to try to bump off Poirot.
We see several shots of a live cobra in the bathroom, then when it falls dead to the floor it's a fake snake, and when the steward carries it and throws it overboard, it must also be a fake. No reason to throw a real one.