Anytime a group of mystery fiction lovers get together eventually the discussion will get around to hard-boiled vs. cozy novels.
The former is the grittier type of novel, taking place on mean city streets, as told by policemen or private detectives. The novels have more physical action, more violence, and more gore. The bad guys tend to be organized crime, serial killers, even terrorists.
Cozy mysteries are named after the tea cozy, used for keeping a pot of tea warm. These stories usually take place in small towns, with bodies often found already dead, and not too messy. The protagonists tend to be amateur sleuths (though not always--think of Christie's Poirot). The bad guys are usually amateurs as well--cases involving domestic murder, embezzlement, secrets that need to be kept quiet.
In hard-boiled mysteries, you'll likely find guns, bombs, knives, and blunt instruments like lead pipes. The bigger the weapons, the better, so big powerful cars are also to be expected. No one in a hard-boiled drives a Smart Car or a Mini Cooper.
Cozy murder victims typically succumb to more genteel methods. Oh, guns aren't out of the question, but they won't be assault rifles or police specials. Maybe an antique musket, or a lady's derringer (I used a Brownie in my last book). A blunt force weapon is more apt to be a fireplace poker or a bust of George Bernard Shaw. If the victim is drowned, it's in the garden pond instead of the East River.
Poisons, though, have always had their place in classic cozy mysteries. One of the experiences that shaped Agatha Christie's career was learning about toxins when she worked in a medical dispensary during World War I. The traditional mysteries are chock full of arsenic, strychnine, and cyanide.
I love garden settings: all someone has to do is mention the foxgloves or oleander in the yard and you know Cousin Horace isn't long for this earth. And certainly the shed out back contains a container or two of rat poison or pesticide.
Like food? Beware of the mushrooms or special herbs Aunt Betsy added to the soup. Or the berries in the tart. Or even certain shellfish harvested in the wrong month.
And let's not forget the exotic poisons--the venom of certain snakes and spiders, the excretions of certain frogs, even poisonous gases that leave no trace. And everyone's favorite, the untraceable poison discovered by a primitive tribe somewhere in the Amazon.
Poisons, somehow, aren't seen as macho enough for tough guys in hard-boiled crime novels. I'm not sure why. The Borgias were the Sopranos of the Italian Renaissance. No one called them wimpy for using poisons. Not to their faces, at least.
So give me a nice un-gritty mystery any day, where you never know what might have been added to the liquid in that pot under the cozy.