Lyric discussion by Cracked-Limbs 

Cover art for Obsessions lyrics by Marina and the Diamonds

I agree with everyone's thoughts about this song being directed on the subject of Obsessive-Compulsive-Disorder (OCD) as a sufferer, this song really touched me. and I listen to it quite often as well.

Marina is not only talking about being having a slightly anxiety related obsession with the 'crackers', but she is also talking about having an obsession with a person, the verse:

"We've got obsessions I want to wipe out all the sad ideas that come to me when I am holding you We've got obsessions All you ever think about are sick ideas involving me, involving you"

indicates that perfectly in my opinion.