Some of these pictures and descriptions may give away plot details that you might not want to know before watching the film.
This is the fourth installment in Disney's Pirates of the Caribbean movie franchise starring Johnny Depp as Captain Jack Sparrow, all of which are loosely based on a Disneyland attraction. Pirates are thieves, kidnappers, murderers, and rapists, so naturally they were the perfect subject for a family ride at Disneyland. They even installed the same ride at other Disney theme parks. The Pirates of the Caribbean ride opened in 1967, but nobody made a movie out of it until 36 years later. (I'm hoping that means there's still a chance I'll get to see the "Mr. Toad's Wild Ride" movie franchise I've been hoping for since I was a little boy.)
In this movie, Jack Sparrow has lost his ship and runs into Angelica (Penelope Cruz) whom he had once seduced in a convent, which he mistook for a brothel, ruining her chance at becoming a nun. She has him kidnapped and put to work on the pirate Blackbeard's ship, telling him that she is Blackbeard's daughter. Blackbeard is competing with Spanish and British ships, all racing to an island to find the Fountain of Youth.
When the ships get to the island they battle an ocean full of beautiful and bloodthirsty Mermaids who quickly overtake and kill everyone on the British ship and sink it. A Mermaid's tear is one of the ingredients needed to take advantage of the Fountain of Youth, along with two silver chalices taken from Ponce de Leon's wrecked treasure ship, and water from the fountain. Depp and company aquire the chalices and catch a mermaid and lug her overland in a glass aquarium on their way to the fountain.
As they are wading through waist-high water in a jungle swamp, Anjelica explains to Sparrow that the ritual takes two people. Both chalices get water from the fountain, but only one gets a fresh tear from a live mermaid. The person who drinks the water with the tear becomes eternally young and the person who drinks the plain water dies. Then they see a snake swimming in the water. Angelica quickly grabs it and continues her explanation. As she tells Sparrow that the person in the ritual who lives gets all the life of the person who dies, she holds the snake inches from his face in a teasing threat as if she plans to kill him right there, but instead she turns around and throws the snake away. (There wouldn't be any more sequels without old Captain Jack.) It's obvious their relationship never was very healthy, and that is proven again at the end when one of them abandons the other on a deserted island.
The snake is a computer-generated effect that is too large to be the type of tropical coral snake it was modeled after. And, as they always do in movies, it has two large fangs at the front of the mouth. Coral snakes do not have these large fangs. This movie promotes the dangerous idea that all venomous snakes have two large fangs, an idea that could be deadly to anybody who thinks a snake is harmless because it does not have fangs. Of course, by the time you're close enough to look inside the mouth of a snake to check out its fangs, it's probably too late to matter if it's venomous or not. And not only is the snake unrealistic, it's not very frightening either. The Mermaids were far scarier. Disney should make another Little Mermaid movie, but with the man-eating kind. I'd watch that.