First, I must say that I am one who believes in ki and the so-called "myths" that surround it. Physically a shinai wouldn't be able to smash someones head. However, if one believes in the stories of Kung Fu swordmasters who can use a stick as they would a sword (blocking the blade of a sharpened steel sword) then smashing heads in is a small step away. If the ki can work in the Iron Shirt/Golden Bell technique, than couldn't one do the same type of strengthening with a bamboo sword, making it like an iron rod?