Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is a fairly predictable romantic comedy that won an Oscar for best original screenplay. There is no actual snake in the movie but there is an imaginative mistaken snakebite section of the movie that goes on for a long time and helps to kindle a romance between a man and woman who at first dislike each other.
Cary Grant and Leslie Caron are stranded for months on a small tropical island in the Pacific at the beginning of WWII along with seven young girls. He's a cranky old drunk and thinks she's a prig, and she calls him a drunken filthy beast, but whenever a man and a woman start out hating each other in a movie, you can usually expect a wedding for them at the end.
One day Caron is out with one of the girls picking berries when she slips into the water and gets two puncture wounds on her leg. The girl sees a branch in the water that looks like a snake and yells that she was bitten by a snake. They return to their hut where Grant puts Caron to bed and cuts the wound then sucks out the poison. (Cutting the bite wounds with a knife and sucking out the poison from a snake bite was a standard treatment for snakebite but it is now considered dangerous and innefective.) Grant has a radio to call in his sightings of Japanese planes and ships. He radios headquarters and asks what kind of snakes are on the island. They find an expert who tells him there are three kinds of snakes and they're all deadly. They tell Grant not to try to suck out the poison like a movie hero, which he already did, so he frantically washes out his mouth.
Grant asks if there's anything he can do. They tell him Caron will die soon and all he can do is give her whisky for the pain. She has hidden all the whisky from him so he gladly tells her it's the only cure for snake bite and she tells him where to find some whisky. They both drink a lot of whisky. She gets very drunk and they tell each other secrets. Grant is secretive about himself, but he assumes Caron's going to die so he's not worried about opening up to her. She thinks it's very romantic that he sucked the poison out of her leg, and the romantic tension intensifies as the seven girls watch through a window.
When Caron becomes so drunk that she passes out, Grant assumes she's dead. He covers her up and gets back on the radio and they send for a priest. Meanwhile, the girl who saw the snake gets angry that Caron died and goes back to find and kill the snake, but she discovers that it was only a branch covered with thorns. She returns with the branch and shows it to Grant, who realizes that it was all a misunderstanding. He goes back inside and finds Caron drunk but alive, radios headquarters, then goes off to sulk and drink more whisky, mad that Caron now knows his secrets. You can almost hear the wedding bells ringing in the distance at this point.