In fact, the two dancers were well known in the Parisian night-life: the woman is Louise Weber, also known with her stage name La Gouloue (the glutton), often portraited by Toulouse-Lautrec and reported to be the inventor of an early form of Cancan; the man his her friend and partner, the dancer Jacques Renaudin or Valentin le disossé, who was so agile that he seemed boneless.
There's a huge sense of movement: the woman's red stockings show off her legs, the figures are defined by curves and nervous lines.
Beside the dance's dynamism, there's also a strong feeling of melancholia that's shown by the soft, cold lighting that distort the figures.