Hours and hours of perusing youtube videos.
Check this guy out!
The guy is really smooth. The cuts are clean.
Although he says he uses the curve of the sword, he does not. The first cut is like...so beautiful! The second diagonal is just like he learned it from his Sensei. After that, his cuts are like baseball bat swings.
So Andy Dean is one of the greats, but I think he got camera happy and decided to show off.