Where their eyes go while you are talking

Eyes that stay on you while you talk mean they are with you. Eyes that leave and come back mean they are nervous about being with you. Both of those are interest. Only one of them is comfortable.

How to read it

The look-away-and-return loop gets misread as boredom constantly, and it is almost the opposite. Somebody who feels nothing has no reason to take the second look — they would simply stop looking. The loop is what caring about your opinion of them costs.

The version worth worrying about is the one where their eyes go somewhere else and stay there: over your shoulder, at a phone, scanning for someone better to talk to. That is not nerves. That is a person waiting for a conversation to end.

When it means nothing

Some people avoid eye contact with everybody, and for a good number of them it has nothing to do with you. If they are exactly the same with their own friends, this tells you nothing at all and you should be reading the other signals instead.

Your move

Test it once by stopping mid-sentence. Nervous interest comes straight back to you. Boredom keeps looking wherever it was already looking.