From his journal…
Dear Neil, In the cell phone pic that Roger Avary took, are you wearing a shiny gold disco jacket, or do you just have a parasite of some kind attached to your back? If the former, you have my sympathies.–Mary Dell
It’s just a red traffic light reflected on the back of the black leather jacket.
I mean, there are no Neptunian Brain Parasites. And if there were, what would one want with me? What you see in the photo is definitely not a parasitic alien brain-slug. No. Why would you possibly think that? Here, come into this small room with me while I press my hand against the back of your neck… See? Now we are united as one in the slug overmind. Is it not wonderful?