Happy Valentine's Day!
This walnut is a simple fractal in nature. Several months ago, I happened upon a television show that was explaining fractals. Since I'd heard the word, but didn't know what it meant, my interest was piqued.
It's a simple, but beautiful concept, really. Fractals involve repeated shapes within the same structure. They can't be exactly the same, or they're geometric, not fractal. The walnut has repeated curvatures of a similar nature that mimic other curvatures within the object. There are more complex fractals, such as a snowflake, a fern, and branches of a tree.
Google has a theme for its iGoogle pages called "Fractals." If you use iGoogle for your homepage, try it. There are some beautiful graphics!