On the singing: dread portion suggests sorcery, no doubt about it.
On the other hand they are at the exact location where sorweel was overwhelmed by the joyous and continuous song that used to fill that location, he even notes how special it was to hear the voices of women and children singing there.
Additionally, the tall has wiped out the consult leadership, and serwe doesn't need to kill potentially powerful allies.
Serwe has been conditioning the mountain with mundane singing for months, there is a huge audience because of the songbird.
Finally, torturer was afraid of her singing because she is dunyain, but he is not afraid of sorcery us singing from her, he gags her and she thinks her plot has gone to shit.
It all seems to add up to mundane singing, but it could just be more lame sorcery rather than clever dunyain tactics.
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