@William – increasing/decreasing volume is a simple way of setting the mood of the music not paricularly the expression of the piece.
Also growling, fluterring aren’t really classed as expression – more like grabbing attention.
To do true expression you need to play the same key and make emotional sounding – like sad & happy etc these are achieved by bending the notes to make them sad sounding and speeding up the tempo to make them more happy….