fruncían
-they gathered
The word fruncían is the imperfect form of fruncir in the third person plural.
See the full fruncir conjugation

fruncir

Meticulosamente evitaba a los que se encontraba por los pasillos, y se dio cuenta de que unos pocos fruncían el ceño cuando él se les acercaba, como si sintiesen que algo estaba mal.
He studiously avoided anyone he met in the halls, and noticed a few that seemed to frown when he came near, as if they sensed something amiss.
Pero por el momento, la fábrica se había detenido completamente. Konomi sentía los ojos de los Kurabito observándola mientras sus hermanos fruncían el ceño ante el documento que tenían a sus pies.
But for the moment, the brewery had come to a full stop. Konomi felt the eyes of the Kurabito watching her as her brothers scowled at the document by their feet.
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