拿一本红色的数或者其他颜色鲜艳的物体，拿着它对着墙。无论书贴不贴着墙都不碍事。

Take a red book or some other brightly coloured object and hold it against the wall.

youdao

As I say, red tends to be chosen, but then if you get lab experiments showing that that particular color of gas blue is somehow or another sort of more invasive of your consciousness than red is, then you move away from the arbitrariness of the choice of red as a color.

所以人们就倾向于选择红灯，但是如果你想用实验证明,比如说烟蓝色或者,其他任何另一种颜色比红色更加醒目，那么你就忽视了颜色选择上的任意性。

耶鲁公开课 - 文学理论导论课程节选