Phase-shifting is the same process behind noise-cancelation equipment and polarized sunglasses.

FORBES: Trick of the Light

In her rearview mirror she could see the guy in the Range Rover glaring at her through his polarized sunglasses and switching his cell phone to the opposite hand so he could give her the finger, but she didn't dwell on his opinion of her for more than a moment.

NPR: In 'Challenger Park,' Mom Is an Astronaut

During a demo, the audience was asked to put on black plastic sunglasses with polarized lenses.

FORBES: CES '09