Yeah. If you look back the past few chapters when she reacts, it's when worms are mentioned.So it was a fear of the worms and not claustrophobia like I thought.
Oh man you might be right. I thought it was odd to have 三 (san) there, totally forgotミ(mi) was a possibility. I thought it was similar to さあ (saa) like Mii's egging Satsuki to do it. Myaan does make more sense in the context.That should read "Myaaan"