I’m not sure exactly how it works, but this is amazingly accurate. Read the full description before looking at the picture.
The picture linked below has two identical dolphins in it. Look at both dolphins jumping out of the water. A closely monitored, scientific study of a group revealed that in spite of the fact that the dolphins are identical, a person under stress would find differences in the two dolphins. People under higher levels of stress see more differences. If you see more than one or two differences, it may be time you took a break.
Now look at the picture very carefully. If you have low stress levels you may need to stare at the picture for quite some time to notice the difference between the two dolphins. The higher your stress levels are the more quickly you will see a difference.
Click the thumbnail to see the whole image.