User blog comment:Dispelling Mage/Omake: Lucy & Migi - Review/@comment-4449950-20150829072752/@comment-7418318-20150829081908

You should put the spoiler in front of your comment... A warning doesn't do anyone any good if it comes after they already read the spoilers.

But I can at least explain Gotou's end. He did control Migi along with all the other Parasites he had in the body, but they were only asleep. When Shinichi stabbed him with the rusty piece of garbage, some kind of toxin entered Gotou's bloodstream.

The Parasites are apparently highly sensitive and vulnerable to toxins. Since the toxin was such a great threat to their survival, their survival instinct kicked in and overrode whatever Gotou did to keep them asleep and under his control. For the others it was just trying to get away in any direction and for Migi it was going back to Shinichi and that little piece of itself that remained within him.