It's just that this Mary lady was eerily calm. Something about her just makes you really nervous. And the preview for the finale kinda leads me to believe that some bad shit is going to happen at Terminus. True that it may not be cannibals, but whatever happens is not going to be all rainbows and sunshine. Not that I really ever expect that in Walking Dead, but I think it's obvious that Terminus will turn out to not be a nice place.