"I'm more curious how one hits a "buried stump" with a bush hog. If it's
buried, it's not an obstacle"

Believe me, it's easy down here in La. Ant hill cover roots, partialy buried crossties and firewood chunks. Did you know that a small block Chevy head will stick up in an fireant hill to get hit by a mower blade? But it just low enough to clear the guard on the front of the mower.