difference between the Percy Jackson books and movies

this has probably been done many times but i wanted to give it a shot. the idea for this will be that i post a difference or mistake each day (hopefully). this will be a compilation of all the difference and mistakes. this is not meant to offend anyone or the actors themselves. this is meant to be a fun book where everyone can share their frustrations or what they liked about the film.
i own no rights to the film or the books.