How do you first feel fear? Do the hairs on your arms lift in a wave of goosebumps? Do your palms sweat--turn clammy? Does your heart jump, and then does your pulse beat like crazy in your throat? Do you freeze in place, too frightened to move?
There are ways to see fear in people. When someone blinks rapidly, or breathes fast--gasping for air. Their voice raises in pitch, or gets an unsteady tone to it. When they shiver without being cold--sweat without being hot, they could be showing fear.
Being a good writer, we don't want to just tell a basic story. That would be dull and almost academic. A good storyteller brings the reader along on an emotional journey with their characters. If our characters are being pursued by a killer, then our readers should be scared for them or we haven't done a good enough job as a writer.
If you'd like a little help on what physical attributes go along with fear, then I'd like to suggest The Emotional Thesaurus -A Writer's Guide to Character Expression by Angela Ackerman & Becca Puglisi. It's been invaluable to me when I've lacked the words to adequately express my feelings. It's almost a cheat-sheet to the emotions.
The next time you’re pondering your writing tools: words, let your mind wonder into the bottom drawer and pull out the emotions that you might’ve been neglecting. It can only make your manuscript better loved in The End.