In the scene where Chunk is being forced into the back of the Fratelli's ORV, notice his mole above his lip is on his right. Now if you pay attention to most of the other scenes(they pull this magic trick a few times) you'll see that it is really on his left. How they do that?! A jumping mole?!
There are lots of ways that this could've been done...It's quite possible that it could be a mirror image where the part where the mole is on the opposite cheek ocurrs, but, being a filmmaker, from experience, I know that there is a more technical and accidental way that this could've happened. The film was accidentally flipped over as the film was being edited. This happened to me back in college as i was doing a film and at one point the house was on the left side and then on the next shot, the house was on the right. It's a simple mistake that can easily occur if the editor isn't paying careful enough attention...It's not like the mole is fake because if you look at the commentary on the DVD of Goonies, Jeff Cohen (Chunk) actually has the mole and it's on the right. Hope this helps.