Final answer:
The pacing of the narrative speeds up when Madame Loisel decides to approach Madame Forestier and identifies herself, leading to quick dialogue and the recognition of the changed Madame Loisel by her friend.
Step-by-step explanation:
The detail that identifies the point where the pacing speeds up in this excerpt is found in the sequence beginning with Madame Loisel's decision to approach Madame Forestier, which marks a transition to more direct action and dialogue. The quick succession of actions and responses between the characters in lines [19] to [26] drive the pace of the narrative forward.
'She went up.' [20] is the moment when the pacing speeds up, indicated by the direct and sudden action taken by Madame Loisel, as compared to the earlier contemplative nature of the passage. Her greeting, 'Good-day, Jeanne.' [21], and the immediate and astonished response from Madame Forestier, '"But-madame!-I do not know-You must have mistaken."' [22], show a rapid interchange that conveys urgency and surprise. The culmination of this accelerating pace is found in the recognition and exclamation from Madame Forestier, '"Oh, my poor Mathilde! How you are changed!"'