What happens involving the Danglars dappled gray horses? why is this significant?

The Count admires Danglars' horses, thus he instructs Bertuccio to offer him the price it will take to buy them. Danglars, of course, a man of business, will sell them to the Count. Monte Cristo has his valet tell Danglars that he is engaged. Danglars thus leaves his calling card, and Monte Cristo returns the banker's visit that evening. He travels there in a carriage drawn by his newly acquired horses.

When Danglars and the Count meet, they discuss a letter from the firm of Thomson and French that opens an account with Danglars for the Count's unlimited credit. Danglars is astonished at this letter. Monte Cristo further astonishes him by presenting two more letters of the same nature. He has unlimited credit with three firms in Europe. Danglars is surprised because he believed himself to have been acquainted with all the major fortunes of Europe. Monte Cristo tells him his fortune is old money, yet money which had previously been inaccessible.

Danglars wishes to present his wife to the Count. Monsieur Debray is currently in his wife's company. The Count met Debray at the lunch at Albert de Morcerf's. Madame Danglars has thus heard of the Count from Debray (her lover) and Albert (betrothed to her daughter). Madame Danglars is astonished, however, when her maid tells her of Monte Cristo's horses. They were, earlier in the day, her horses, and now they are attached to the Count's carriage. She blames her husband, a creature of profit, for selling her prize possession. Two hours later, after his departure, Monte Cristo sends the Madame a letter and returns the horses. He even inserts a diamond on the rosettes that they wear on their ears.

The next morning when Madame de Villefort and her son take a ride in the carriage drawn by Madame Danglars' prized dappled grays, the horses become wild. They pass the Count's Auteuil residence, where Ali, the Count's valet, is conveniently located and equipped with a lasso to save the mother and son. The son has fainted. Monte Cristo pours a drop of liquid in the child's mouth, and thus the child is rejuvenated.

Analysis:

This chapter witnesses the Count winning favor with the wives of both his archenemies. He plays with Danglars' desire for money, by buying his wife's horses from him, not because he actually desires the horses, but because he wishes to win Danglars' wife favor. He does this by returning the horses to her. This gesture also astounds and intimidates his enemy because the Count essentially throws away the huge sum of money for which he bought them. His ploy also widens the domestic schism that already exists in the Danglars' household, for husband and wife do not live in happy matrimony.

The Count also wins the trust of Madame Heloise de Villefort. By "saving" her from the wild horses, and rejuvenating her son, Madame de Villefort is so impressed with the miraculous Count. He knows the story will be related to her husband who will feel obliged to visit the Count. This is how the Count schemes to meet his nemesis.