Sadger are invisible and have never been seen by any human, or by any bears.

Sadgers are notoriously un-catchable. Some say this is due to the fact they are invisible, but most tend to agree upon the fact that it is just that they are not visible.

Sadgers are not badgers, nor are they bears.

Sadgers are simultaneously 0% and 300% water at all times.
Scientists might have thought that this may be behind their ability to be invisible, and would run tests, were it not for the fact that no-one has seen one, nor the fact that they wouldn't be able to catch one.