Season One, Episode 6 - Secret Sex....when Samantha and Carrie are hanging the poster of Carrie (for her column) at one point you can see them hanging the poster and its flat...as they are tacking it, when it shows it again you can see that one corner of the poster is curled up and when it pans back again to the same shot it is lying flat again. Simple slip up, but noticable none the less.