Muck You!

There are a lot of members of the animal world who effectively communicate by displaying colors or markings. Squids behave like the deep sea equivalent of a mood ring by turning colors to reflect their mood. While in the human world we can't turn a brilliant shade of puce to express ourselves, a vigorous game of "I'll show you mine if you show me yours" usually gets the message across. People at a poker table can communicate subtle messages just by displaying cards, or in many other cases, failing to show them.