A local man, Tom Carmody, pays a visit to Thedy, the wife of Charlie. Tom casually enters Thedy's bedroom and they start making love. Meanwhile, Charlie is visiting a local carnival. He's fascinated by a sideshow display that consists of nothing more than a jar with some strange creature, apparently dead, floating inside. The carney-boss admits that neither he nor anyone else knows what it is, but everyone is intrigued by its existence. He offers to sell it to Charlie for $40 and the farmer accepts. Charlie takes it and explains that he hopes to attract the attention of his neighbors. As he puts it in Charlie's truck, the carney-boss warns that it's been nagging at his mind recently and he's glad to be rid of it.
After sex, Tom admires Thedy's bird tattoo on her arm. She ushers him out but tells him that he's welcome to come back any time.
Charlie stops at the local grocery store and asks if they want to see the jar. Tom mocks him but the other townsfolk come over. They're fascinated by the brief glimpse but Charlie quickly leaves. However, he makes sure to invite them to his house to see it later.
When Charlie gets home, he shows the jar to Thedy. She isn't interested and walks away. Charlie talks to the thing in the jar, explaining that Thedy takes all of his money and is often gone visiting her out-of-state relatives. Thedy walks off, saying that she doesn't need him. Charlie is reluctant to see her gone, until he notices that the townsfolk have come to see his jar. They gather around and eventually start speculating on what it is. Opinions vary, and one man thinks it's a swamp creature while another thinks it's a kitten that he drowned. Charlie is content to have people there, paying attention to something of his.
Thedy parks with Tom and they work out which "out of town relative" she'll be visiting while she makes time with Tom. He wonders why she stays with Charlie, and Thedy explains that Charlie doesn't try and keep her confined. The two of them discuss the jar.
At the house, Charlie keeps the discussion going. A woman suggest that it's her dead son that died in the swamps, while a man thinks it's some prehistoric predecessor of mankind. They all jump when someone shouts that it moved, but Charlie insists that it's dead. Tom and Thedy return and Tom insists that it's just a bunch of jellyfish. Charlie says he's jealous but Tom insults him and leaves with Thedy. The townsfolk finally wrap it up for the night, but Charlie tells them that they can come back any time. However, once he's alone, he isn't nearly so confident.
Later, Charlie is trying to sleep when Thedy comes in, laughing. She finally tells her husband that she and Tom went to see the carney-boss, and he told them he made the "creature" out of old rat bones, pig eyes, silk, and rubber bands. Charlie tries to cover his ears but Thedy insists on telling him everything. Her husband finally blames her and Tom, saying they've been laughing at him for years, and he figures they're going to tell everyone what the jar-creature is. Thedy says she won't, but Charlie figures she already set out to ruin it for him and she's succeeded. Angry, Charlie looks at the jar and then calls Thedy over. Realizing something is wrong, she backs away and Charlie advances on her.
The next night, the townsfolk visit to talk about the jar. Charlie tells them that Thedy has left to see her relatives. However, Tom comes in, with no idea where Thedy is. Charlie just smiles at him, while the townsfolk discuss the fact that the jar-creature has apparently changed its eye and hair color. Charlie insists that it's just the same, but Tom notices a bird tattoo on a patch of skin. He looks nervously at Charlie, who smirks at him and says that they'll never know just what it is.