Getting smudges inside the screen has happened to other Tamagotchi versions, and is probably a general manufacturing error as others have concluded. The only way to get rid of it would be to open up the Tamagotchi and wipe it off, perhaps with a cloth as to not get particles on the rest of it. I feel that as long as you don't lose pieces and screw everything back together tightly, you should be fine. I've taken an Angelgotchi (a vintage tama) apart and screwed it back together and it works fine. I've also taken a Tamagotchi Dream Town Friends apart and although it works fine, it wouldn't close properly so I had to put tape over the gap in the plastic. Since the mini is likely more similar to a vintage Tamagotchi than a modern one, it will likely stay together better than my Dream Town.