Board Thread:Speculation House/@comment-27684451-20160128020900

So in Vol. 3 Chapter 7, after they get Mercury into the ambulance, Emerald gets a headache saying "One mind I can handle, but two is a stretch." Who else besides Yang was she using her semblance on? She only needed to make Yang see it, and Mercury wouldn't need to, so who else was she tricking? Why did she have to trick Yang and said person at the same time? 