You're cruising at standard speed, safe from the car ahead of you and nothing but converging lines behind you in the mirror.
You glance up again and in your rearview are eyes and teeth. The eagle glare of the new Dodge Charger headlamps is distinctly predatory. Or maybe it's the gleaming grille of a Denali flexing itself against your personal automotive space. It's a Spielbergian moment: turning to see the T. rex in your face.
Whoa. Stress hormones flood the bloodstream, eyes widen, your heartbeat jumps. Can you easily move left or right and get out of its way? Is it weaving and charging, looking for a way to slice around your left or right bumper? Which will it be? Grip and hold steady until it backs off or roars into another lane.
Calm down and go on. You still gotta drive.