sumi-e, japanese painting, chinese painting,
On their thousandth birthday deers turn white.
That explains why a white deer is a symbol of longevity.
So where does the happiness come from?
From a peculiarity of the Chinese language.
The word for happiness (fu) happens to be the same as the word for bat (fu).
Logically, whenever you see a painting containing a white deer and bats—if it is in English—it means “Oh Dear, you are going batty!”;
but if it is in Chinese, it means “A Thousand Years of Happiness”.
The bats, by the way, are dancing around the moon.
Some personages have complained that those thingies look suspiciously like ink-spots.
These people lack true understanding.
Those are BATS!
If I say so.