In [TPOD: 2, Unweaving, 82], Moridin is waxing wroth on things which the Third Agers can do which were not known in the AOL:
"A way to Heal being severed.... Involuntary rings. Those Warders and the bond they shared with their Aes Sedai.... whenever he thought he had the measure of them, these primitives revealed some new skill, did something that no one in his own Age had dreamed of."
Quite a few people have expressed confusion over what "involuntary rings" are; here is an explanation. A "ring" is a way of referring to a group of linked channelers (such a group has been more commonly called a "circle"). In [TPOD: 2, Unweaving, 83], Moridin wonders about the repercussions of Ny's group using the weather ter'angreal in "a ring"; the implication being that he's wondering what would happen if they used it in a circle. Thus, an "involuntary ring" refers to channelers being linked against their will. We've seen this done, and know the device which makes it possible--the a'dam. The mention of involuntary rings is a reference to the damane, who are linked to the sul'dam involuntarily.