In the mediaeval period there was no real percieved difference between real and mythical animals, after all, much of the world remained unknown and who was to say what strange and magical creatures existed in distant lands? Nevertheless, real animals A Complete Guide to Heraldry, A.C. Fox-Davies, Bonanza (re-print of 1909 Edition), New York, 1978, P191 are perhaps one of the most common sights on coats of arms, especially animals of European origin. The rat Is a typical example of these and certainly no negative connotations should be taken from its appearance, it is a cunning and hardy creature!