Just like fingerprints. The tongue is a unique organ in that it can be stuck out of the mouth for inspection, and yet it is otherwise well protected in the mouth and is difficult to forge. Perhaps in the near future, we will use tongue prints...say aaaaahhhhh
At this very moment I know full well you are putting this fact to the test…now remove your thumb from your nose and pass this on to the friends you think might be interested in comparing their thumbs to their noses as well.