FIG. 1 is a perspective view of a mascara brush, showing our new design; FIG. 2 is a lateral view (left side) thereof; FIG. 3 is a lateral view (right side) thereof FIG. 4 is a rear view thereof; FIG. 5 is a front view thereof; FIG. 6 is a top view thereof; and, FIG. 7 is a bottom view thereof.