Once you've gotten your point A to point B and you've cleaned out, following that ribcage, you're just going to take your knife and keep following that line. You can see the knife kind of running up to the pin bones. The pin bones are pretty soft, but you may need to crack them a little bit. You can hear them. You don't want to really ruin meat. You just want to crack those through.
Then, once you get down to there, what you'll see, especially down by the tail, is a little bit of a white line, and that white line is actually the spine. So we're now going to take our knife gently, pull the meat back and jump the spine. Tilt the knife and pull back. That will come right up. Sometimes it's easier to start down by the tail and work your way up just because it helps you kind of find the guide.
Then, when you get up to the pin bones, again, just give them a good crack. Sometimes you can twist the knife a little bit, or just saw it back a little bit, and that should open right up for you. Down to the other side, following the rib cage, and your fillet should fall right off for you.