When I first made this a few years ago on a Lenovo Thinkpad, running it would quickly hang Chrome. Technology has advanced in the meantime, and I've limited both the area and number of iterations so you should be safe.
The idea came from seeing a short video explaining that you could implement a reaction-diffusion system in Photoshop by chaining filters, and then at some point finding out that the SVG spec allowed filters too.
It's slightly randomised each time!
Feel free to adapt and remix of course