There are two sides to every coin, right? Yes, there are. Well, warmth is the other side of the freezing cold of winter. This poem is about being cold, but also about getting warm. Logs for a fire, a guy blowing on his "nail," and a pot of stew that is too hot to eat—all images of warmth amidst the coldness of winter. All the warmth in this poem symbolizes the persistence of life amid the desolation of winter—the ways people find to keep on keepin' on during a very difficult season.
Line 2: A guy blowing his hands (okay, he's blowing on his fingernail) is an example of synechdoche, which to us seems like a sure symbol of winter. It's also a way of keeping warm.
Line 3: Clearly the "logs" are for a fire, and they make us think of warmth and coziness. It's possible that "logs," given their close association with fire, are an example of metonymy, putting us in mind of the warmth they give off while burning.
Line 9: A "greasy" woman standing over a pot definitely makes us think of a warm meal—some type of comforting soup or stew. Apparently, the meal is a little too hot because "greasy Joan" has to stir it a little bit to cool it off.
Line 14: The image of a "roasted crabs" in a "bowl" echoes and foreshadows the image of "greasy Joan" over her pot. Something that is "roasted" is warm, and also probably very savory. Even in winter, nice, warm beverages (the "bowl" of apple) are to be found.
Line 18: As before, the "pot" that "greasy Joan" is stirring ("keel") makes us think of a nice, hot meal, perfect for a cold, winter's day.