How to Practice Your Side Eye, 1913

The muscles of the eyes may be strengthened by slowly moving the orbs from side to side and also by bending the head a little forward and rolling them up and down. One does not want to practise this too many times; the eyes need to be stimulated, not fatigued.

Marie Montaigne, How to Be Beautiful

One does not want to practice this in public, either. Train those orbs in the comfort of your own boudoir before you give the world the side eye.