Fanchon was showing him a new step, which she taught her next partner in turn, continuing instructions during the dancing.

The children crowded the floor, and in the kaleidoscopic jumble of bobbing heads and intermingling figures her extremely different style of motion was unobserved by the older people, who looked on, nodding time benevolently.
Fanchon fascinated girls as well as boys.

Many of the former eagerly sought her acquaintance and thronged about her between the dances, when, accepting the deference due a cosmopolitan and an oracle of the mode, she gave demonstrations of the new step to succeeding groups, professing astonishment to find it unknown: it had been "all the go," she explained, at the Long Shore Casino for fully two seasons.

She pronounced "slow" a "Fancy Dance" executed during an intermission by Baby Rennsdale and Georgie Bassett, giving it as her opinion that Miss Rennsdale and Mr.Bassett were "dead ones"; and she expressed surprise that the punch bowl contained lemonade and not champagne.
The dancing continued, the new step gaining instantly in popularity, fresh couples adventuring with every number.

The word "step" is somewhat misleading, nothing done with the feet being vital to the evolutions introduced by Fanchon.