The original Prius design was very conventional: https://commons.wikimedia.org/wiki/File:1st-Toyota-Prius.jpg
The second generation is the well-known streamlined shape: https://commons.wikimedia.org/wiki/File:2008_Toyota_Prius_(N...
(I think the shape was probably not a mistake on Toyota's part. A lot of people were buying them partly because they wanted other people to know they had them, and the shape indicated this very clearly.)