Ravan was a very intelligent character in ramayan people viwed him as having ten heads it does not mean ten head mounted on single neck and
having twenty eyes ect . normal creation of god man usess only 5 to 6%
of brain one among us who usees more than say 10% becomes intelligent
in such terms Ravan was master of so many vidhas of life during that time
for normal person it was impossible to bealive that a normal person can master so many things and that is why it is said that he must be having ten heads