Steven Pinker

They know that you know you're experiencing it.

Tears, you're looking at the world through a scrim of fluid.

It blurs your vision at the same time that other people can see the glistening or the trickle.

So again, you know that you're crying.

Other people know that you know that they know.

And eye contact is the ultimate common knowledge generator because you're looking at the part of the person that's looking at the part of you that's looking at the part of them that's looking at the part of you ad infinitum.

Although you don't have to think about it ad infinitum.

Why should that mean anything other than what it means?

Well, Darwin dealt with that in the book where he noted that some facial expressions are...

vestiges or remnants of facial postures that animals do when they're about to attack or they're defending themselves.

So in the case of the fear expression, he noted that if you're likely to be a prey animal or someone who's going to be picked on by the alpha, you've got to open your eyes wide to see where threats might be coming from.

If, on the other hand, you're the predator or you're the alpha... You want to focus.

Exactly.

And if you...

The remnants of that include, and so the furrowing your brows, which I think narrows the field of vision.

It may even narrow, if the folds of skin actually intrude on the pupils, might increase depth of field.

Going back to these nonverbal common knowledge generators, we use them to make something public that formerly was private.

That's the common denominator.

Yes.

So in the case of eye contact, now that developed way before we were humans because among primates, eye contact is a threat signal.