QUALITY ARM IS QUALITY.

She's cupping her own nub with the inverted hand of a third, invisible arm. But if it's a third, invisible arm, who's to say the hand connected to it is inverted?

Well, I can see how it's not a third arm - that hand is supposed to be her left. Trouble is, the artist failed the perspective on this one.

I'll leave it without the error tag, but if anyone else thinks it's justified, feel free.