Explain how the reference to Mr. Johnson's anger being "like a poison" contributes to our understanding of his action in "Like a Winding Sheet."

We know that Mr. Johnson endures a lot of physical pain from the daily labor he performs, and on the particular day that the story takes place, he was also treated with cruelty and degradation by the female boss at work. After work, the waitress seems to treat him rather rudely. And then, at home, his wife, Mae, is actually being nice to him, but because her words and actions remind him of the previous conflicts, Mr. Johnson snaps and beats Mae. 

We want to understand, then, why Mr. Johnson did this. Mae certainly didn't deserve it, and it's violent and frightening.

Considering how Mr. Johnson's anger was like a poison definitely helps us sympathize with him. A poison works its way into your body and perhaps into your mind as well, and it damages you from the inside out, if not right away, then slowly.

That's what was going on during Mr. Johnson's day. The pain in his legs that seemed to seep outward into the rest of his body on the subway ride, the awful accusations and racial slur that his boss hurled at him, the furious anger that built up even more when he mistakenly believed that the waitress was denying him his coffee just because he was black--all of this was "poisoning" Mr. Johnson's spirit, making him feel more and more angry, to the point where he was "ill" in his mind and unleashed that anger and bitterness on his wife.

In fact, if you have a close look at the story, the narrator often refers to Mr. Johnson's anger as something that he can't control: something that's seeping into his body, taking over it and forcing him to do its bidding. This, too, helps us understand his violent actions even if we can't condone them.

For example, notice how he experiences his anger as a physical "tingling" in his hands, a tingling that continues to spread (like poison) throughout his body.

Also, look at the description of Mr. Johnson's thoughts as he's actually beating Mae: he feels appalled at himself, horrified, and yet he feels that something inside him is "holding him, binding him to this act." That something is the "poison" of anger.