Sometimes cosplayers/otaku will also wear a cat ear headpiece or accessory accompanied with a choker/collar with a bell on it. The word "nyan nyan" is commonly used in japan to decribe the noise a cat makes. To seal the deal, often they will say the phrase "nyan nyan" while taking the picture and smiling.
2. A sound a used to describe the noise a cat makes. Commonly used in Japan.