The shelf / Never / Russian

RUSSIAN

Когда рак на горе свистнет.

“When the crayfish whistles on the mountain.”

MEANS

Never.

Tails first

The oldest English version, from 1616, says pigs fly with their tails forward. The film took that literally.

Source: Fedorov, Phraseological Dictionary of the Russian Literary Language; Wiktionary.

On the label: When pigs fly

Watch it

The film: “This pig has been flying backwards since 1616”

The same idea, elsewhere

From “When pigs fly” to Russian.

ENGLISH, 1616Pigs fly in the ayre with their tayles forward.The oldest form.John Withals' dictionary, 1616 edition (Phrase Finder).
FRENCHQuand les poules auront des dents.“When hens have teeth.”Académie française, Expressio.
RUSSIANКогда рак на горе свистнет.“When the crayfish whistles on the mountain.”Fedorov; Wiktionary. A river crayfish, not a crab.