Really? Lightly touch an icon but don't press hard enough to show the shortcut menu - as you modulate your touch pressure the glow will follow. When you peek an email, adjust the pressure of your touch - you will see it zoom in and out.
Within a few minutes of playing with the feature it was obvious that it was very high resolution detection of pressures.
https://medium.com/@rknla/exploring-apple-s-3d-touch-f5980ef...