Title text:
People looking for the gaps in our understanding where the meaning of consciousness or free will might hide often turn to quantum uncertainty or infinite cosmologies, as if we don't have breathtakingly complex emergent phenomena right there in our freezers.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3144/
See here and here You need like a particular temperature and the ice crystals to grow with the right orientations from the edge inward and meet in a triangle in the middle.