A town in Poland had only one cow and it stopped giving milk. 
The townspeople did a little research and discovered they could 
get a cow from Moscow for 2000 rubles - or one from Minsk for 
only 1000 rubles. So, naturally, --- they got the cow from 
Minsk.

It was a great cow: had a wonderful disposition, and gave lots 
of milk and lots of cream. Everybody loved it dearly. The people 
decided they would mate the cow and get more cows like it, 
and then they would never have to worry about their milk supply 
again.

So they got a bull and led the cow and the bull into the pasture. 
When the bull came in from the right to mount the cow, the 
cow moved to the left. When the bull moved in to mount the 
cow from the left, the cow moved to the right. This went on all 
day.

Finally, in desperation, the people decided to go ask the rabbi 
what to do. After all he was very wise.

They told him the story. "Rabbi, we've tried all day to mate our 
cow. When the bull moves in from the right the cow moves left 
and when the bull moves in from the left the cow moves to the 
right. What do we do?"

The Rabbi thought a moment and asked, "Did you buy this cow 
from Minsk?"

"Rabbi!" they replied as one, "You are so wise! We never said 
we bought the cow from Minsk. How did you know that?"

The Rabbi said, sadly, "My wife is from Minsk."