What is visceral? It is the bodily happenings when someone is experiencing an emotion. When you include that in your writing, it gives the reader a sense of reality and connection with your characters.
Let's see how John, my temp MC, reacts to this sentence:
The creature, eyeless in the deep night, slithered closer; death in its breath.
John fell and screamed, unable to move.
John fumbled, his hands like blocks of trembling ice, his feet leaden things that weighed his heart to a standstill.
Do you illicit visceral reactions in your characters?