Answer:
What word has kst in the middle, in the beginning, and at the end?
A mighty weapon in the war against winged household pests.
My first master has four legs, my second master has two. My first I serve in life, my second I serve in death. Tough I am, yet soft beside. Against ladies cheeks I often reside.
Bury deep, Pile on stones, My mind will always Dig up them bones
Gets rid of bad ones, short and tall. Tightens when used, one size fits all.
I have two bodies joined together as one. When standing still I run and run.