The simile curse tells us that the scalp fell to the ground, but Mormon never provides that detail. He does tell us the effect of this curse, however, and that is to convince many of the Lamanites to surrender their weapons and enter into a “covenant of peace.” The reason for this change of heart is likely centered in the significance of the scalp.
In Maya artistic representations of captivity the hair of the head is becomes symbolic of capture, with many of the captives being grabbed by the hair on the top of their heads. The scalping is also indicative of capture. Thus what the Lamanites may have been seeing was a symbol of the surrender of their captain, and therefore their army. They would have seen the lifting of the scalp as an indication that Zerahemnah was a captive. Once the leader was captive, the entire army could be considered captive as well.
Of course Zerahemnah had not surrendered, and his personal will to fight will continue this fight. The point is not what Zerahemnah intended, however, but the way in which his men would have seen the raising of his scalp.