Depends.
First off peoples eyes wander during tests. It happens. Thats not good enough reason in my
book to turn someone in for cheating. If you catch someone staring at someone paper over and
over, thats a different story.
However, if you find that students end up with common wrong answers. Like they both got 3,4,7, 9
wrong. And they did the exact same things wrong, and the mistakes are same for those problems.
I would consider turning them in. Because in that case the cheating is apparent.
Turning someone in for cheating is one of those things you don't want to be wrong on.