Yeah, it's not something that's supposed to be there, but don't mind it so much. At least the lines are even and not jagged. If you see the Twintwist in Kmart Footscray, it's helmet looks like it'd been haphazardly carved out with a knife (I didn't bother taking a photo since I no longer use photobucket, but it's been there for about a week now). This defect on Slugslinger kind of adds a bit of character to the toy (somewhat reminds me of the Joker), but if it ever reaches a point where I can't stand it anymore, I guess I could try to paint over the lines around the mouth. I think it's there because the paint they used was applied too thinly.