"Of course," he said dryly, "and cows might fly, too -if they had wings."

"It's a good thing cows don't fly," they say with an evil chuckle.

Which meant when cows fly.

In Finnish, the expression "kun lehmät lentävät" (when cows fly) is used because of its alliteration.

I had to bring her over from Miami today because the stupid cow won't fly.

And why do they say that cows fly in outer space?

When cows fly, Ben thought dismally.

Now I'm told it can't be put back on until hell freezes over and cows fly.

"Maybe cows will fly over the castle," Abernathy grumbled.

A cow, lifted by the wind, flies past the spectators.