These sonic waves kept drilling into the heads of Daniel and the millions of civilians, forcing them on the ground, to vomit the contents of their stomachs, as well as bleed from the ears and scream in pain. Yet, no sound could be heard.
Even if Daniel had been able to think, he would have not been able to understand what was causing all of this. After all, the attack was auditory in nature, and was exclusive to civilizations which had developed through the use of technology, instead of cultivation. That was the power of ultrasounds.