LOL @ Jonathan!!
For what it's worth, I never took that as a threat, as it appears you are. I took it to mean that God is going to be praised whether we give it to Him or not. If the rocks cry out, it means just that: the people didn't praise so the rocks did instead. I don't know of any hidden meaning in that, nor do I perceive a threat. God will be praised no matter which of His creations give it to Him.