I'm sure you've seen programming koans more than once. But for the longest time I couldn't understand what is really meant when people talk about the answer not being significant, but how you arrive at it. But sitting on the toilet today, and pondering the ``Does a dog have Buddha nature?'', it finally clicked.
The Dog is very important to this. To see why, let's modify this koan a little:
``Does The Sussman have Buddha nature?''
This is bad, for a simple reason. When you read this, you will be naturally inclined to ponder nature of The Sussman himself, not that of Buddha. The Sussman gives you an out to not really reflect on the Buddha himself, but instead trying to find qualities in The Sussman that match your vague understanding of what Buddha is.
But when we ask ``Does a dog have Buddha nature?'' we do not have that crutch anymore. If you start reasoning about a Dog, you will soon come short, because a Dog does not match the greatness of The Sussman, or Buddha. Therefore you will be pushed to think of what ``Buddha nature'' is instead. As you reflect on that, you will come to understand Buddha, and the principles he embodies on a deeper level. That is the point of this koan. It does not matter if Dog has a Buddha nature, the point is to make you consider what would be Buddha nature. This is what people mean when they say the answer to a koan does not matter.