Here's a demo of the one in your eye - it will work with the right eye too, except to be effective it would have to be a mirror image:
The thing is, people have the same sort of "blind spot" in their mind, except it blocks out information, and they fill in the blanks with their imagination.
This is probably because looking at what's really there is way, way too scary - "Monsters from the Id", and all that. ;-)
Thanks, Rich