Title text:
They're up there with coral islands, lightning, and caterpillars turning into butterflies.
Transcript:
Transcript will show once it’s been added to explainxkcd.com
Source: https://xkcd.com/3135/
"The earth tilts when the moon hits far end of earth during moonset and that's why there is low tide. A high tide happens during moonrise when the moon drags it up slightly."