When Del is driving the wrong way and the couple in the other car is trying to make them aware, Neal looks at the side of the road and sees some snow and then realizes that in fact they are going the wrong way.
I don't grasp what is it that makes him know. What I'm supose to see in that short image?
Here is the clip of the scene
He’s not looking at the side of the road, he’s looking at the median. Notice how he looks down at the space between the two cars, and then he looks back up at the other car.
The median (the space between the two directions of traffic) was on the right side of the car. It’s supposed to be on the left side. The snow is on the median.
The other car is on the other side of the snow. The snow is on the left side of the other car. That means that the other car has to be in the correct travel lanes. If the other car is going the right way, then their car must be going the wrong way.
