This mug has been infused with the deepest mountain magic known to yetis. At first, it looks like a boring old black coffee mug. But bring it into Yeti's Post, and fill it with some of our hot coffee, and a secret message will be revealed. Note, only works with coffee you buy from us, otherwise, who knows what sort of profane message this sorcery might reveal. • Ceramic • Black matte finish when cold • Reveals the print when exposed to hot liquids • Dimensions: height - 3.85" (9.8 cm), diameter - 3.35" (8.5 cm)