Answer:
Who is he that runs without a leg. And his house on his back?
My first half is normally made of stone, my second is crazy, and I taste sweet when complete.
I run through hills. I veer around mountains. I leap over rivers. And crawl through the forests. Step out your door to find me.
Add a T and I shoot through the sky. Then add an S and I multiply. What word is it?
It is a sound of empty, speak and it'll talk back plenty. But all the more you yack, you'll get the same words back.
You use it between your head and your toes, the more it works the thinner it grows.