Did they screw it up? Hypoxia causes convulsions, that’s a well known fact, so I don’t get all the fuss about witnessing normal body functions in a dying body. Especially as people convulsing are unconscious.
The real torture here – and with all death sentences – is the years and decades long psychological torture while on death row. And rspecially in this case of course the first, botched execution attemped. Ramming needles for four hours into someone!
/dev/fb0 is the framebuffer. So yes, you can feed data into the filesystem and you’ll see it on your display.
For Unixoids, being a file does not mean that this data is stored on a hard disk, but that all data, processes and hardware are accessible with the same toolkit. /dev/fb0, for instance, is part of the file-like interface of your graphics card.