
If you're gonna post a spoiler in the first place, might as well post the context of that spoiler. Otherwise you're just ranting about a fake nail.

Spoiler.....
Was thinking the same. Sangwoo looked like he was testing Kwak to see if he would keep his promise and leave them alone. Of course Kwak failed. So now we're left to wonder wants going to happen to him in the next chapter.

He's probably bored or an adrenaline junkie and wants to provoke the adrenaline rush by playing the classic psycho's game of "let's see whose smarter here" with the police.

what if- he purposely wanted to get caught so he could blame bum and get him taken away so he no longer suffers? because in the last chapter he did say bum is the one who makes him suffer and he wishes he killed him.

That's just too angsty for sangwoo. I think he put the nail there on purpose. He knew kwak already suspects him and thus decided to kill him.
Finally, we got the old sangwoo back!! Can't wait for the next chap!
OK who thinks sangwoo dropped the fake nail in purpose?
There is no way it could be there after all those months after her assassination.