I was in the bathroom, thinking about the difficulties in the latter part of Prufrock, after the five lines. If I were to diagram the journey Prufrock is on, the figure would be a pyramid, rising to this climactic point in the poem, then falling away, a triangle, a pyramid. Having thought that, I suddenly understood why he choose the sea creature, "a pair of ragged claws." This sea creature moves backward, as if away from something: up to this moment, down and away from this moment:
"Shall I say, I have gone at dusk through narrow streets/And watched the smoke that rises from the pipes/Of lonely men in shirt-sleeves, leaning out of windows?...
"I should have been a pair of ragged claws/Scuttling across the floor of silent seas."
Ah. "And how should I begin?" That's it. The preceding experience of walking through the streets of fog and smoke is all he has to offer to a relationship. The loneliness of the men in shirt-sleeves reflects his own isolation and loneliness, the men leaning on window sills, perhaps, and watching life passing them by. That detail from his journey to that room is not much to offer to begin a relationship. So he lets the moment slip away from him, says nothing. The next two lines convey the resignation of being unable to act. Prufrock, like the backward moving lobster/crab, has already let the moment for beginning the relationship pass, and like the sea creature, Prufrock is looking back at the moment of opportunity as the moment recedes. He was wrong about time, he should have realized, for the time is suddenly not in the future; the time is now, and the moment has just passed. The "ragged claws" is a wonderful image in this context, for with the claws he would have had something tangible to grab the moment and hold on. But time is not tangible, as we all know, and thus the moment is lost to him. The seas are silent because there is no sound of real conversation from him, and water, I think, is an image of meaningful reality (love is real even if I am cut off from it). Remember, the journey takes him to the beach, the edge of the sea, where the journey ends one way or another: asleep/awake; life/death; dryness (sawdust, oyster shells)/water (the ocean); "the women"/sea girls; etc.
But everything in the poem has led up to this central moment, and now everything that he thinks about after this moment is a consequence of failing to act, or of being incapable of acting. Thus, Prufrock begins the process of identification, rationalization, and justification.