a herring

I promised jokes. Here's a joke I think of as hermetic, because only old school Jews get it.

Two old friends, out of the same shtetl, met a couple of times a week for tea in Manhattan, always the same time, same place. Sp they're sitting there, as they always did, staring into their tea cups because everything they had to talk about they'd already talked about. Finally, one of them looks up, still a little dreamy from the tea steam but rising on the wings of an idea. "Okay, Shimel" he says, "wot's green and you hang it on the vall and it vistles."

Shimel is still mostly in his tea cup, but slowly he raises his head, half dazed, half quzzical, and says, "Green, you hang it on the vall and it vistles? How should I know because there's no such thing. C'mon, you tell me." So Chaim, the first man, replies, "A herring." Shimel's astonished. ""A herring?! A herring is green?" Chaim says, so you pain it green." "Okay, okay, a herring, a herring hangs on the vall?" Chaim, simply, "So you hang it on the vall?" Now Shimel is getting exasperated. "So now you gung tell me a herring vistles?!" Chaim lets the moment hang, then, "So it doesn't visel."