Answer:
You use a knife to slice my head but you weep beside me when I am dead
I am rarely touched but often held and if you are smart you'll use me well.
I regularly change shape yet remain a sphere. I am always there but not often seen. What am I?
I go around in circles but always straight ahead never complain no matter where I am led. What am I?
I destroy your home from the inside out.
If all Wibbles are Criggles, all Borkins are Kwumblins, no Hoggles are Borkins, and all Criggles are Borkins, is it true that all Borkins are Criggles?