Everyone was looking at their own shoes
What the room is actually doing
Take the café from chapter 1 and look at it from the ceiling. There's the couple, who are in the middle of a conversation about whether to go to his mother's on Sunday, and the man with the laptop, who's on a call with his camera off and is trying to look as though he's typing, and the two women laughing, who are laughing at a message one of them got, and three people alone with phones, and one with a book. You walk in. What happens.
The couple don't look up, because the mother question is live. The man with the laptop sees movement and his eyes flick and go back to the screen, because he's being asked something on the call. One of the two women glances over because you passed close to her bag, sees a person, and turns back, and the other never looked. The three with phones are with their phones, and the earlier book Look up is about how completely a phone takes a person out of a room. The one with the book might be the person most likely to notice you, and they're the person you'd have minded least.
Boothby, Clark and Bargh open their 2017 paper with the coffee shop, the waiting room and the bus, and their point is the one this whole book has been circling. Each of those people is, to some degree, watching the room. And each of them believes, wrongly, that they're watching more than they're watched. Which means each of them is also under their own beam. The man with the laptop is sure the room can tell he's not really typing. One of the women is sure her laugh was too loud. The person with the book is wondering whether sitting alone with a book looks affected. Every person in the room is the main event of their own afternoon and a passing shape in everyone else's.
It's like being in a cinema and worrying that the audience is watching you instead of the film. They're watching the film. Every one of them is the film. The room, from the ceiling, is a set of people each looking at their own shoes, and you walked through it worried about yours.