In the middle ages some viewed the serpent in Eden as being Lilith, a demon who was believed first by the Babylonians. She is actually much more ancient than the character called Satan.
She is still carved into a church in france in the above picture.
Many bible stories were believed many different ways through the ages by many different people. The modern consensus just seems certain to many because it just happens to be popular and fueled by many strong feelings.
Ancient scripture beliefs varied wildly before the modern era. Its amazing how few Christians seem to recognize this.