Octopus walking up on land: really cool video

This video shows an octopus as it walks onto land and proceeds to walk a significant distance (for an octopus) apparently to a crab it either saw (how could it see it from under the water a distance away?) or smelled (I looked it up and they can smell, but again how would it do that from under the water?). This neat event was caught on video by a family that was visiting Fitzgeral Marine Reserve where it took place--though accounts indicate that it is not rare for an octopus that live near shore to walk on land it is just uncommonly observed and they were at the right place at the right time and with their video camera rolling. There is an interesting discussion with an expert here on the Scientific American blog. SeEtta