If you lie down on the ice and begin to crawl, this will spread out your weight more evenly and make it less likely for the ice to suffer a critical failure, in which you might fall below the surface of the ice and into the water. You have better weight distribution by being on more than two points - only your two feet. By crawling you disperse your weight to possibly up to eight points or more. This includes hands, elbows, knees, feet, chest. The dispersing of the weight takes significant pressure off of just one or two points, because as you are walking you are also most likely lifting a foot. By crawling, you remain in constant contact with your weight spread more evenly.
