How Many People Are Necessary to Create a Collision?

Wy raises the question, how many people are necessary to create a collision? Is it one, or is it two? It's at least two. I mean, you could have more, i guess. But what this study found is that people are constantly monitoring for upcoming collisions and then adjusting their walking trajectories accordingly. Several meters in advance. What rules do they use to make those those evasions? And this just apparently happens constantly. We're usually not even aware of it. Don't even really think about it. The taboo against touching other people while you're walking,. or basically the force that keeps you separate from other people and makes you want to avoid running into them or touching