So I have a sweet stout that has been sitting in the secondary for about a month, patiently waiting for me to bottle it. All airlock activity stopped about three weeks ago. Then, suddenly, bubbles started appearing in the beer. There isn't really any airlock activity but there is a small ring of carbonation-like bubbles at the top and you can see plenty of bubbles rising up. Has the ferment picked back up for some reason? Or has some alien invader rendered my precious brew undrinkable?