The Gadiantons were dressed to terrify, and when they saw Nephites falling to the ground, they supposed that they had achieved their objective and did terrify the Nephites. Mormon tells us that the falling to the ground was rather a supplication to God. We know that there are other modes of prayer among the Nephites that do not require prostration on the ground, but it appears that there was one mode, perhaps that involved in the most desperate of supplications, that did include prostration. In many cultures, the prostrate position is a sign of humility, and it may be seen in this context in this action of the Nephites.