Sneak's eye, Kyoto, Japan
This is a tiny cup for drinking Japanese sake and the pattern inside is popular for us. When we drink it, we use this type of cup or non-pattern cup. Sake masters usually use it to check the clearance and color and the pattern seems to makes the nature more visible.
By the way, the pattern is called 'sneak's eye', Janome in Japanese, and also have a meaning to keep evil sprits away. So using this pattern is very reasonable because the Sake is thought to be very pure, sacred and religious and often used for shrine's ritual.