This story takes the reader to a carnival side show and to "one of those pale things drifting in alcohol plasma . . . with its peeled, dead eyes staring out at you and never seeing you." The protagonist of "The Jar" is Charlie, a man so charmed with the jar that he persuades the carnival owner to sell it to him. When he takes the jar home, Charlie's poorly constructed living room becomes a palace and the jar becomes it emperor. Folks from miles around come to his shack to sit, stare, and philosophize over his jar. Strangely, however, each person who looks at the jar sees something different in it. No one can seem to agree on the thing's eye or hair color, and the thing seems to move; it even seems to change. Moreover, each individual sees in the jar the manifestation of some deep evil, some dark and secret sin, or some hidden guilt. To Juke Marmer, the thing in the jar represents a horrible childhood experience; as a child, he drowned a litter of newborn kittens. But Mrs. Tridden sees within the jar the form of her three-year-old son Foley, whom she lost in the swamp. Thedy, Charlie's unfaithful wife, peers into the jar and remarks that the thing in there looks just like Charlie. Charlie is tired of her infidelity to him and murders her in order to end her whoring. Afterward, when Charlie looks at the jar, he, like the other townsmen, finds the thing familiar. Certainly now, at least, Charlie's wife will never wander from him again.
As one of the finest examples of Bradbury's macabre writing, "The Jar" sets the tone for the many so-called carnival stories that were to follow. In these stories, carnival imagery is the major source for Bradbury's discussion of the presence of evil as a threatening force in the world. "The Jar" reveals Bradbury's belief that the potential for evil as well as for good dwells within each person. The evil nature of the jar is suggested early in this story when the carnival boss admits that he has been having strange thoughts about the jar. Then, the night meetings at Charlie's are described as a "kind of rude church gathering" where the townsmen sit with "reverent awe" gazing at the jar. Also, the embryo in the jar is depicted as being a "Holy Grail-like thing." Here, then, the nature of religious worship is juxtaposed with the implied evil nature of the jar, indicating that either of the two is possible. Yet the fantasies that the characters engage in concerning the "thing" in the jar indicate that for them, evil is so strong that it has taken precedence over the good. Implicit is Bradbury's warning that this disguised evil can be a potent possibility unless humanity is careful to cling to that which is good.