The tongue which is an important internal organ is encased within the oral cavity and well protected from the environment.
The tongue is made up of groups of muscles and is pretty tough. It is interesting to note that the tongue works 24 hours even while we are sleeping; especially to constantly push saliva down the throat. It also helps to mix and process foods.
In addition, it binds and contorts itself to form letters when a person is speaking. It also contains linguinal tonsils to filter out germs when a person is sleeping.
It has unique features which differ from one individual to another individual and even between identical twins.
The uniqueness for each person is mainly the dorsal surface of the tongue. Digital photographs of the tongue can be captured and matched with a database for verification.
They can also be used to identify the shape of the tongue. So, if you want to hide your identity, do not stick out your tongue.