Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
We don't see a snake in this movie, but a bite from a snake we don't see is the catalyst for a romance. This is John Frankenheimer's cold war masterpiece about U.S. military war prisoners who were brainwashed by the North Koreans who sent one of them home to be used as a political assassin.
Two of the former P.O.Ws, Major Marco (Frank Sinatra) and Raymond Shaw (Lawrence Harvey) have been drinking one night. Shaw tells Marco about the time before he went into the army when he met Jocelyn, the love of his life. He was lying on the ground feeling helpless after being bitten by a snake "afraid to move because you're not supposed to move, it makes the poison circulate, when unexpetedly, there she was with a razorblade in her hand." She gets off her bicycle and excitedly starts to attend to the wound on his ankle. (It looks like she might have cut the wound with the blade then massages it to get some poison out instead of sucking it.) She tells him that her father will be very pleased to find out about the snake bite because he is so afraid of snakes that he makes her carry around a razorblade and a bottle of potassium permanganate solution so she will be prepared in case a snake bites her. She takes off her shirt to wrap it around his leg and that seems to be all it takes for Shaw to fall for her. (He asks her father for permission to marry her shortly afterwards.) She takes him to her father's house where he is pronounced OK. (It must have been either a dry bite or a harmless snake.) The father then recommends the traditional folk remedy against snakebite - alcohol no doubt. We find out that the father is a U.S. Senator who is the mortal political enemy of Shaw's domineering mother (Angela Lansbury) and her senator husband, but that only encourages Shaw to date Jocelyn seriously until his mother forces them apart.