"There are a couple of things in there if we're constraining this discussion to horror here"

This quote by Eddie Campbell suggests that there are a few topics within the scary category that are worth going over. He implies that the conversation should be restricted to horror, as there are a few things that are worth checking out within this genre. This might imply that there are specific aspects of horror that deserve discussing, such as using suspense, making use of dive frightens, or using gore. It might also mean that there are certain scary films or books that deserve discussing, such as The Shining, The Exorcist, or Frankenstein. Campbell's quote implies that there are a couple of subjects within the horror genre that are worth exploring, and that the conversation should be restricted to horror.