Sang-woo is scared, keeps counting the pills, confides to Bum basically that knowing your loved one has betrayed you is worse than the physical pain, tells Bum, without mentioning his mother directly, that she told Sang-woo that he would die a painful death. Sang-woo reverting to his childish coping of burying himself under Bum's top, flashback to toddler Sang-woo drawing his mother on his bedroom wall, and her walking into the room smiling, Bum is acting more like the mother and is telling Sang-woo to wait and he'll find out, the pills keep getting revisited, as it seems whatever Bum's bought is hiding there, Bum knocks them over and sweeps them back into the pot which presumably led to a few going missing, Sang-woo during the night goes and counts the pills again, and discovers there are some missing, he ends up distraught thinking that Bum has poisoned him, and this is the big gift that Bum is referencing.
Bum just says "you'll find out soon" and keeps going into that basket of drugs, which is obviously making Sang-woo paranoid, and getting flashbacks/fear relating to his mother. "Bum, do you know how to kill someone without killing them" relating to the betrayal of someone you love/trust betraying you, and conveying his fear about such, and that Bum might do the same again. It seemed like Sang-woo thought Bum was "surprising" him with trying to kill him. Why Bum can't just be honest about whatever he picked up at the shops, who knows. Guessing it might be an Xmas present, which might account for the secrecy and time delay.
Is a new chapter coming out today?