Shibuya Crossing, Tokyo
Shibuya is a neighborhood in Tokyo that is known for its dense population: Over 14,000 people per square kilometer. The Shibuya crossing is often cited as the busiest intersection in the world. It is a particularly dramatic sight to see the hundreds of people crossing from multiple directions. They are often avoiding each other as they push through the sea of people in front of them. You can see videos of this crossing here and here.
Imagine for a moment that you were crossing the road and wanted to make a eye contact with everyone you passed! You would quickly fail. How do pedestrians in such a situation acknowledge each other?