Nice catch!
Here is a very quick video on "cleaning" them!
Cleaning BlowfishUsing the rake makes it easy. Basically, it takes place of your fingers. I always cleaned them on a board with a nail too. We would nail the head to the board, make the cut behind the prominent bone in their head, straight down like they did in the video. Then where he put the rake in, use both your fingers and pull. Should come out and look like meat in the video.
I can't ever get a straight answer out of ANYONE, including scientists and marine biologists, but the northern puffer could be slightly toxic like others in that species. The toxins could be in the skin, liver and intestines...so make sure you get all the skin off and don't try and gut them. No use finding out if they are toxic by not cleaning them properly.
Enjoy!