Walton would bring up a few points.  Among them being, the misuse of other physical related reactions, incorrectly stipulated to be fear, or simply that if they were to truly suspend belief than they would once again resort to the behavioral equivalent of someone in fear, and therefore call for help, fight or flee, etc. 

The misuse of other physical reactions to a physical work of fiction can sometimes be misconstrued to be legitimate or authentic fear.  For example, the adrenaline kick a person gets in the climax of a horror film could be described as fear, when it is simply adrenaline.  Being startled, surprised, or fearing other things can also be in Walton’s words, quasi emotions, or quasi fear. 

Fear of other things can be substituted for fear of or for fictional characters as well.  For example, one might be afraid of the dark, or the concept of mysterious origins, and misplace that as fear for the green slime.  Perhaps the fear of  the concept of being murdered is sparked by viewing a horror film in which a character is murdered.