Black Teeth's Back

Have you ever noticed that in commercials every single person has perfectly white (and straight) teeth and then you think to yourself, "those people are a bunch of UGGOS and they should make their teeth BLACK instead of PEARLY WHITE"? Well, the first thing you should do is probably not refer to others as "uggos" and the second thing you should do is hop in a TIME MACHINE and travel back to the DAYS OF BLACKENED TEETH AS A BEAUTY STANDARD! Before we get to the purely silly FASHION-FOCUSED teeth blackening, we're going to learn a quick history lesson. Specifically about Japan during the HEIAN period (8th-12th centuries). Nobody quite knows when exactly the practice of blackening teeth started, but it has been narrowed down to sometime during that VERY LONG SPAN OF TIME (helpful, I know). For your first CODE, figure out what the Japanese practice of blackening teeth is called and THAT IS YOUR CODE! No searching the catalog necessary... I mean, you CAN if you WANT, but I don't think you'll find much.