User blog comment:IamJakuhoRaikoben/Chapter 498: Gray vs Invel, Review./@comment-26389992-20160823003306/@comment-7418318-20160823094915

Sure it is all about mind-control, but that doesn't seem to work right off the bat going by Juvia's thoughts, so there might still be a few seconds for Gray and Juvia to act before they are completely under the sway of the chains.

But I wonder... will breaking the chain that links them together really remove the entire spell? They'd still have the collars around their necks after all.

So it might be useless, with the linked chains just being symbolic and limiting movement, while the real magic is in the collars (Mavis also has a collar with just a shot chain dangling form it), it might dispell the effect entirely, or it might be something in between.