@tarrentella, I actually tried that before I posted and it didn't look right. The reason is there is no edge on the "lips", so he looked like he didn't have lips which is horrifying lol!
I have another picture of this sackboy and you're correct that the inside of the mouth is also knitted. But since he has "lips", I know the creator did some sort of binding off and then picked it up to finish the inside of the mouth.
It's just strange that mine looked like :|
But it could be the way she stuffed the head that created a little contour on the lower lip...
@abbily, yeah it's a sackboy