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 dark comedy with lots of bloody violence but the scariest thing about it is the racism. It feels a lot like a Coen Brother's movie because they were two of the screenwriters.
In the 1950s, the first African American family to move into an all-white suburban neighborhood called "Suburbicon" is harassed and then violently attacked by their all-white neighbors. Their young son Andy befriends his next door neighbor Nicky, a boy about his age. After Nicky's mother dies, Andy offers to give him a "ground snake" that he takes out of his jeans pocket. Nicky accepts it. When Nicky asks if the snake bites, Andy says it doesn't because it has no teeth. He says it eats grasshoppers or crickets and he gives Nicky a large jar to keep it in.
Much later, when a gangster is trying to abduct Nicky from his hiding place under his bed, we see the glass jar break and the snake crawling away under the bed. A few minutes later we see the snake crawling over the dead body of one of five people who get murdered in the house that night in a crazy orgy of revenge, greed, and stupidity.
The snake (some species of gartersnake or ribbonsnake) is obviously used to show a common bond between two boys that transcends the racism of their parent's world, but later when it escapes, it's not frightening or funny, so it might be used here just to illustrate how the boy's world has shattered, like the jar. Or not. It's confusing. The next day when Nicky's house is still filled with bloody dead bodies, and Andy's house has been trashed and his parent's car burned up, Andy and Nicky play catch in their backyards as if nothing had happened.