One important symbol in "Sweat" is the snake. Beyond its obvious association with the devil, it symbolizes the aggression and violent patriarchy that oppresses Delia.
Delia is upset when Sykes brings home a rattlesnake. Its status as a symbol of evil and temptation is made explicit when Delia addresses it as "ol' Satan."
Snakes are associated with male violence and power. When Sykes drapes his bull whip over her shoulders, Delia is frightened and asks Sykes if he remembers she is scared of snakes. He says of course, that's why he did it, and he reacts to her fright with "mirth" or laughter. From the start we see the hold has over her: she is one of the few things in life he can feel superior to.
It was sadistic of Sykes to scare Delia with his snakelike whip and more sadistic when he brings home a rattlesnake, knowing his wife's fear of the animal. Delia's and Sykes's connection is symbolized by the snake, with its potential aggression representing Sykes's threatened aggression against his wife. When Delia turns in anger on the snake, this foreshadows her turning on Sykes himself. When the snake is frisky after eating frogs, Delia
did not run away with averted eyes as usual. She stood for a long time in the doorway in a red fury that grew bloodier for every second that she regarded the creature that was her torment.
The creature becomes a stand in for Sykes, who is her true tormentor.
Yet this symbol of patriarchal power comes back in the end to destroy Sykes, not Delia: when the poisonous snake bites him, Delia uses the passive aggression she has internalized over a lifetime and lets him die without offering a helping hand.
The snake as a symbol coordinates with the overall theme of the story that both Delia and Sykes are victims of white oppression, which is enabled by patriarchal violence. Sykes might try to mimic this violence, but in the end he is helpless against it.