Japanese idioms of improbability


I'm sure most (English speakers) have heard terms like:

> when pigs fly

or

> when hell freezes over

or

> when the Cubs win the World Series **[obsolete]** (U.S. only)

Am wondering if there is anything similar in Japanese.

Wikipedia has a list but nothing for Japanese:
[List_of_idioms_of_improbability](https://en.wikipedia.org/wiki/List_of_idioms_of_improbability
"List_of_idioms_of_improbability")




You can find many idioms that denote something is impossible on online
glossaries, including:

  * 石に花咲く (a flower blooms on a stone)
  * 太陽が西から昇る (the sun rising from the west)
  * 網の目に風とまる (wind being trapped by a net)
  * 畑に蛤 (finding clams in a vegetable field)
  * 山の芋鰻になる (potatoes becoming eels)

But these are all fairly rare. I think these are used like `(impossible event)
なんて (idiom) だ/(の)ようなものだ`. As far as I know, none is widely used in the form of
"～の時に", "～たら", etc. Saying 石に花が咲いたら仕事します, for example, will only confuse
people.

