The cage has a body (10) comprising two sides (11, 12) that are defined in two opposite parallel planes (14, 16). A blade (20) is rotatably mounted on the body about an axis of rotation (21) between a position (P1) and another position (P2). An element (30) is driven in rotation relative to the body about another axis of rotation (32) such that rotation of the element rotates another element (24). The axes are arranged parallel to each other in a plane parallel to the two planes, where the axes are located at predetermined distance to each other. The blade is entirely contained in a space delimited by the two planes in the former position, where two end parts (22, 23) of blade emerges the space in the latter position.
