Certain words can change the pacing and tone of a story. Take my examoles below, I'll write the same passage but with different tones.:
1: His breath slowed down as he gazed up twoards the building. Covered in vines and showing signs of decay, he felt his heart start to race. 1 beat, 2 beats, 3 beats; he could taste the fear rising in his throat. But he knew what he had to do. So with a determined step, he clung to his sword and walked forward.
This passage has a slower pace, it dosnt cause she sense of panic, but it dose cause the reader to wonder what will happen next. The word choice and pace are slow and steady.
2: His breath hitched; he was alone. He let his gaze rest upon the decerept builiding.
Vines weaver in an out of broken windows, decay littred the outside. He felt his heartbeat slow in his chest.
3 beats
2 beats
1 beat.
He tasted the salt of his fear. But they were waiting for him
Waiting for him to succed.
He breathed in, out, in, out.
He grasped his sword, setting forward twoards the doorway.
Here the pace is a bit faster and the word choice makes the reader a bit nervous. Word choice and pace are tools used to affect the readers reactions to situations.