I was reminded of this episode because the novel was made into a black and white movie and this scene is briefly shown (with split-second nudity). I learned about this movie because it was posted here! Here is a link to the movie scene:
https://youtu.be/5Ua4mTo1TBo?feature=shared&t=248
In Émile Zola's l'Assommoir, two women fight in a wash-house with clothes-beater. One of them manages to overpower her opponent, pins her to the ground, bares her bottom and paddles her vigorously.
https://gutenberg.org/cache/epub/8558/pg8558-images.html
https://gutenberg.org/cache/epub/6497/pg6497-images.html
If you wonder what a clothes beater is:
https://www.si.edu/object/NMAI_142693
https://www.etsy.com/listing/962302495/vintage-laundry-beater-solid-wood
I don't know who did the English translation shown below, but it seems somewhat bowdlerized. Zola mentions explicitly that the woman lifts completely the other woman's skirts, tears away her pantaloon and displays "everything, the naked buttocks, the naked thighs". The translation just mentions lifting the skirt and showing "white and naked skin'".
I also suspect that "everything" may allude to the fact that if an adult woman is bared in this way and shakes away violently, as happens here, she displays her genitals or, at least, her pubic hair.
FRENCH TEXT
Elle avait un visage si terrible, que personne n'osa approcher. Les forces décuplées, elle saisit Virginie par la taille, la plia, lui colla la figure sur les dalles, les reins en l'air; et, malgré les secousses, elle lui releva les jupes, largement. Dessous, il y avait un pantalon. Elle passa la main dans la fente, l'arracha, montra tout, les cuisses nues, les fesses nues. Puis, le battoir levé, elle se mit à battre, comme elle battait autrefois à Plassans, au bord de la Viorne, quand sa patronne lavait le linge de la garnison. Le bois mollissait dans les chairs avec un bruit mouillé. A chaque tape, une bande rouge marbrait la peau blanche.
— Oh! oh! murmurait le garçon Charles, émerveillé, les yeux agrandis.
Des rires, de nouveau, avaient couru. Mais bientôt le cri: Assez! assez! recommença. Gervaise n'entendait pas, ne se lassait pas. Elle regardait sa besogne, penchée, préoccupée de ne pas laisser une place sèche. Elle voulait toute cette peau battue, couverte de confusion. Et elle causait, prise d'une gaieté féroce, se rappelant une chanson de lavandière:
— Pan! pan! Margot au lavoir… Pan! pan! à coups de battoir… Pan! pan! va laver son coeur… Pan! pan! tout noir de douleur…
Et elle reprenait:
— Ça c'est pour toi, ça c'est pour ta soeur, ça c'est pour Lantier…
Quand tu les verras, tu leur donneras ça… Attention! je recommence.
Ça c'est pour Lantier, ça c'est pour ta soeur, ça c'est pour toi…
Pan! pan! Margot au lavoir… Pan! pan! à coups de battoir…
On dut lui arracher Virginie des mains.
ENGLISH TRANSLATION
With almost superhuman strength she seized Virginie by the waist, bent her forward with her face to the brick floor and, notwithstanding her struggles, lifted her skirts and showed the white and naked skin. Then she brought her beater down as she had formerly done at Plassans under the trees on the riverside, where her employer had washed the linen of the garrison.
Each blow of the beater fell on the soft flesh with a dull thud, leaving a scarlet mark.
"Oh! Oh!" murmured Charles with his eyes nearly starting from his head.
The women were laughing again by this time, but soon the cry began again of "Enough! Enough!"
Gervaise did not even hear. She seemed entirely absorbed, as if she were fulfilling an appointed task, and she talked with strange, wild gaiety, recalling one of the rhymes of her childhood:
"Pan! Pan! Margot au lavoir,
Pan! Pan! à coups de battoir;
Pan! Pan! va laver son coeur,
Pan! Pan! tout noir de douleur
"Take that for yourself and that for your sister and this for Lantier. And now I shall begin all over again. That is for Lantier—that for your sister—and this for yourself!
"Pan! Pan! Margot au lavoir!
Pan! Pan! à coups de battoir."
They tore Virginie from her hands.