Here is a fine expression about flax, typical of the rich imagery of Breton: Hennezh zo mad da frikañ bolc’h (that chap is only good for stamping on flax) = he is a horrible dancer, he steps on his dance partner’s feet. This alludes to the times when people danced on flax capsules in barns to tread out the seed and it was an opportunity for neighbours to enjoy getting together.
Frikadeg bolc'h, Ar volc'hadeg (stamping on capsules, to get the seeds out)
Until the 1930s, the operation involved in beating or treading flax seeds out of their capsules was an occasion for real fun and entertainment. After retting (and sometimes before that), flax was combed. The capsules separated from the stems were then laid out to dry, either on the ground of the barn, the floor of the granary or even of rooms in the house. On a September or October evening, the ground of the barn was carefully swept clean, then boards were set up over the threshold on the entrance side high enough to keep the seeds inside so they could be swept up and the well-dried flax capsules were spread out in a layer about 20 cm thick. Then the whole neighbourhood (ar c'hontre, that is, the nearby farms that provided mutual help for threshing grain, as well) was invited to come beat them out by dancing, so the seeds burst out of the capsules under the pressure from the dancers’ feet.
Dancing on the new threshing floor in Penmarch, Collection Andrieu (Morlaix), public domain, Creative Commons.
NB this postcard photo provides a taste of the atmosphere, and may have been to prepare the floor for flailing wheat or another cereal, but is not dancing to beat out flax seeds. Earthen floors in houses were prepared in much the same way. This was called in Breton plas an ti newez and la pilerie de place in Gallo (one of oil languages of the northern half of France, spoken in Brittany east of the north-south line there, while Breton was spoken west of that, generally).
As musical accompaniment, the dancers usually had singing by one of the participants, which was taken up in chorus by all the others. Sometimes there was a whistler, like Lom Kerboriou from Brelevenez in the Trégor in northern Brittany, perched on a barrel, who led the dancing. At other times, there was a violin, accordion, humming into an ivy leaf, a comb or cigarette rolling paper to carry the dancers away in a saraband.
Flax capsules by Rasbak - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=7542276.
In Ploubezre in the Côtes-d’Armor département, also in the north, people remembered François-Marie Derrien, whose nickname was Cousin (1874-1938) and who led this kind of evening, as the saying goes - gant e violons koad o vont en-dro 'vel ur ribod (with his wooden violin working like a churn). Cousin even became legendary. People say that coming home from one of these evenings, he was caught in a trap with a wolf and that he had to play his violin and sing all night long to keep the animal calm, because it threatened him every single time he stopped. That is why he sang Biken ken, biken ken / Cousin na sono da den (Never again, Never again / Cousin will never play for anyone again).
Stanis Derrien nicknamed Cousin (coll. Daniel Giraudon).
In the barns, people often did French dances like quadrilles, polkas or lancers. Less often, they did rounds as to the song Plac'hig an douar nevez (The Girl of Terre-Neuve, Canada). In fact, considering what the objective of the exercise was, they did not really dance, they stamped on the capsules. That is why some of the lady dancers, when asked if a fellow knew how to dance, replied with the expression Ya,...frikañ bolc'h! Yes, he knows how to stamp on flax!
Daniel Giraudon, emeritus professor of Breton, Université de Bretagne Occidentale, researcher at the CRBC (Centre de recherche bretonne et celtique), Brest.