Because it's a movie. Werewolves aren't real, either.

A werewolf is terrorizing the small town of Tarker's Mill, Maine ...only no one knows it except for 11-year-old Marty Coslaw (Corey Haim) and his 15-year-old sister Jane (Megan Follows). With the help of their Uncle Red (Gary Busey), Jane and Marty, who is confined to a wheelchair, attempt to identify and kill the werewolf.

Silver Bullet is based on the Stephen King novella Cycle of the Werewolf (1983). King also wrote the screenplay.

Silver Bullet has a double meaning in the movie. It refers to the only way a werewolf can be killed, that is, by being shot with a silver bullet. It also refers to the motorized wheelchair, the Silver Bullet, that Uncle Red builds for Marty.

They were simply playing poker and using baseball cards as the chips. That's why they had the rule "You can't bet managers".

Yes, Wolfsbane, also known as monkshood or aconite, is a member of the Aconitum genera, which consists of over 250 species. Aconitum is poisonous, and the various species have long been used for hunting and for medicinal purposes.

This question is not addressed in the movie. In the book, the werewolf was created when s/he came upon a strangely beautiful flower in a cemetery, but the flowers turned black and died when picked, indicating that there was something supernatural about them. Some have suggested that the plant was wolfsbane and cite the famous line from The Wolf Man (1941) (1941) where a gypsy woman announces, Even a man who is pure in heart and says his prayers by night may become a wolf when the wolfbane blooms, and the autumn moon is bright. The supposition is that werewolves in King's story are not created by the bite of another werewolf but by contact with a certain flower. In other werewolf legends, it's when the victim is bitten or scratched but left alive that they turn into a werewolf themselves at the next full moon.

Finally convinced that Marty might be right about the killer being a werewolf, Uncle Red takes Marty's silver medallion and Jane's silver crucifix to Mac's Gun Shop and has Mac, described as an "old world craftsman" and a "wizard of weaponry", fashion a silver bullet. He then arranges to get Marty's parents out of the way the night of the next full moon, which occurs on Halloween, by giving them tickets for "a romantic weekend in New York" under the guise that he won them from Publisher's Clearing House. That night, Red, Marty, and Jane sit up together, waiting for the werewolf to come after Marty. Come 3AM, Red is about to give up and send the children off to bed when Jane sees the werewolf lurking outside the living room window. Suddenly, the lights go out, and the werewolf smashes through the wall, causing Red to drop the gun. The silver bullet goes rolling down a heating vent. While the werewolf tosses Red around the room, Marty fishes for the bullet, loads it into the gun, and shoots the werewolf in his other eye. The werewolf crumbles to the floor and slowly turns back into the reverend. In the final scene, the three of them huddle together on the floor. Jane asks Marty if he's alright, and Marty replies, "I don't think I can walk." Marty then tells Jane that he loves her, and Jane says the same to Marty. In a voiceover, adult Jane says, "I wasn't always able to say that, but I can say it now. I love you, too, Marty. Good night."

Those who have both seen the movie and read Cycle of the Werewolf say that the stories are similar but the storytelling is quite different. The book is divided into chapters, each one corresponding to a month in which the werewolf emerges during that month's full moon and is often centered around the various holidays throughout the year. The cycle begins in January and ends on New Year's Day whereas, in the movie, it begins in the Spring and ends on Halloween. The movie is told from Jane's perspective and centers around her brother Marty, whereas the book doesn't even introduce Marty until halfway through. Oddly enough, Marty in the book does not have a motorized wheelchair. There are other differences in the victims and the way the werewolf kills them, but these are minor.

Doing an IMDb search on the keyword "werewolf" will call up over 500 movies, too many to be listed here. A good place to start might be with Werewolf of London (1935) (1935), one of the first werewolf movies ever made. It features the same artist who did the makeup for Larry Talbot (Lon Chaney Jr.) in Universal's seminal werewolf movie The Wolf Man, which was remade in 2010 as . Other werewolf movies that have significantly added to the genre include The Howling (1981) (1981), An American Werewolf in London (1981) (1981), Wolf (1994) (1994), and Ginger Snaps (2000) (2000). Although not exclusively about werewolves, the series of movies following Underworld (2003) (2003) and Twilight (2008) (2008) have also added immensely to the genre.