Authors:

Then - as he was talking - a set of tail-lights going past lit up McMurphy's face, and the windshield reflected an expression that was allowed only because he figured it'd be too dark for anybody in the car to see, dreadfully tired and strained and frantic, like there wasn't enough time left for something he had to do.

Ken Kesey (2012). “One Flew Over the Cuckoo's Nest: 50th Anniversary Edition”, p.231, Penguin
Then - as he was talking - a set of tail-lights going past lit up McMurphy's face, and the windshield reflected an expression that was allowed only because he figured it'd be too dark for anybody in the car to see,