This is not seen very often, but does show up once in a while. Your opponent goes through the entire pre-shot routine, with practice strokes. Suddenly, he seems to lose confidence in his stroke.
He shifts his bridge hand over to the side and tests the shot with full follow-through. This is repeated several times and the bridge hand is brought back in line with the shot.
A variation of this is to perform the practice strokes, and suddenly stop. He might make a minor adjustment of of his bridge hand or the height (follow/draw) of the stoke, and then resume the practice strokes.
Once he gets ready to actually shoot the shot, he seems to be ready to stroke the shot, only to not commit to the stroke. This can be done several times before the shot is actually executed.
If you are closely following his shooting, there is a slight tightening of your muscles as he telegraphs the intent to stroke. When he doesn’t do this, there is a small mental reaction.
Doing these several times can exhaust your mental preparedness. These can be unconscious attempts to make sure the stroke is dialed in rightly, and can indicate an obsessive desire to make the shot right.
You might get fooled a few times on this trick. If you allow yourself to pay attention to his shot, you can get distracted.
The easiest way to handle this is by placing your attention elsewhere – even closing your eyes works. Wait for the click of the balls to bring your attention back to the table.