Just type ~=[,,_,,]:3 in your Google+ chat window and you will see instantly see a running nyan cat. Possibly this is the first of the undocumented emoticon for Google+ chat. And we believe more will be revealed soon just like we have discovered hidden Gmail chat emoticons.
Unfortunately, this works only for Google+ chat and not for Gtalk or Gmail Chat. However, we have other secret emoticons like V.v.V for crab, }:-)for devil, :(|) for monkey and many more for Gmail chat or gtalk gadget mentioned here. (via)
