In order to apply mascara and comb they eyelashes, the invention proposes carrying out a selective, clean and adaptable cutting of the bristles twisted along a core by selecting some of the bristles located, along the wire, in angular sectors of adjustable amplitude and by continuously cutting the bristles thus selected at a predetermined height. The implementing guiding module has a guiding inlet head (69a) and a cylindrical tube body (69c), the head being for bristles remain curved. The cutting (70) and guiding (45) groove formed by an end piece with a conical outline extended by a hollow tube having a central channel (31) of the same diameter, cutting (70) and guiding (45) grooves being formed in the channel. The cutting grooves (70) are distributed longitudinally in order to select the brush bristles to be left untouched, alternating with the grooves (45) for guiding brush bristles to be protected from being cut, the cutting grooves (70) forming, in the tube body, cutting slots (57) and guiding grooves (45) having a depth such that the selected grooves from indentations (45a, 74a) on the end of the end piece. The present invention is mainly applicable to the cosmetic industry.