Bias is in the air In the whisper of the trees Bias is in the air In the thunder of the sea Just for you I loaded up the episode again to check what Georgiou is saying ("You should know, I've magnetized the spore cube. Enjoy." ) So they explicitly tell you what she was doing at the console after she lured Leland there and trapped him in the spore chamber. I also did what I was too lazy to do in my original post and checked in which episode Spock kills the other puppet of Control. It was In the Valley of Shadows. So they expected the audience to be able to retain the information that you can defeat such a puppet with strong magnets for two episodes/weeks. And it's not like it was a blink and you miss it minor detail that would be unrealistic to expect people to remember, it was a pretty big scene. I had not watched In the Valley of Shadows since it aired before watching the final episode, and I had no trouble whatsoever to understand what Georgiou was doing once she said she had magnetized the chamber. Because it wasn't just two "random pieces of dialogue". They showed us in action what strong magnets can do to the nanites, so that Georgiou could do it again without us being completely confused as to what is going on (provided we paid attention). That is classic setup and payoff.