Board Thread:Speculation House/@comment-33053086-20171210163906/@comment-27082610-20171212050811

The two prevailing theories are:

1) Exactly what Qrow said, they're for use on Grimm, and the reason Cinder was affected is because she used the Grimm beetle to attain her powers and may still have it inside her.

2) They're anti-magic. This also fits due to the fact that the Grimm are a product of one of the gods, one of the same that gave Ozpin the power he later bestowed upon the maidens.

Both have their own merits, and at this point, it's honestly impossible to tell which is more likely.