What" merciful" terms does Twala offer Ignosi's army if they surrender?

From the text:

‘I will have mercy and be satisfied with a little blood. One in every ten shall die, the rest shall go free; but the white man Incubu, who slew Scragga my son, and the black man his servant, who pretends to my throne, and Infadoos my brother, who brews rebellion against me, these shall die by torture as an offering to the Silent Ones.’ Such are the merciful words of Twala.”