Responses

I just binged all of this and the drugs weren't from the apple juice itself. remember in a flashback from the mom's perspective in the earlier chapters she was surprised that somyeong performed CPR on her brother? mom already qknew somyeong knew, and so gave somyeong a "choice" by retrieving the apple juice and purposefully tainting it and seeing if somyeong will report her.
Both morphine and propranolol are really bitter and bad tasting and if they were all over the straw he absolutely would have tasted it right away--plus it would take a couple of mL of solution to do the trick, so how did she manage to get that into him with just a straw? O_o On top of everything else, apple juice can mess with the absorption of beta blockers. Mom would surely have known all of that, especially if she was planning a pharmaceutical murder! Maybe Mom was giving li'l bro propranolol regularly *before* the fateful day ("here, for your 'anxiety' my son") so that he wouldn't taste whatever she doped the juice with? Propranolol can alter your sense of taste, though it's not a guaranteed side effect. Could that be why he was so into eating sour candy--'cause nothing else tasted like anything by that time??
edit: I wonder if Mom gave Myeong Jin blood pressure medication to keep him kinda listless and drowsy--remember how Somyeong said after the bike incident that Myeong Jin got really quiet? It's weird too b/c Somyeong was the one with anxiety and a rapid heartbeat. If anyone needed propranolol in that house it was her! There are so many ways this could go, I'm really curious about what happened; I hope we get a new chapter soon!