Un mouton à cinq pattes

Juliette wasn’t just looking for a roommate. She was assembling a mythical being. Someone who vacuumed unprompted, loved plants but never overwatered them, paid rent early, had the emotional intelligence of a therapist, the cooking skills of a Michelin chef, and the personal footprint of a ghost. Oh, and no weird smells. Naturally, she was chasing un mouton à cinq pattes; the legendary five-legged sheep, last seen dancing the tango with a unicorn on top of the Eiffel Tower during a blood moon. A creature so rare, Indiana Jones gave up halfway through the search.  But Juliette was undeterred. After all, if dragons exist in books and men can wear socks with sandals, surely her dream flatmate was out there… probably trapped in a time loop or hiding in a Lidl.

The French phrase "un mouton à cinq pattes" literally means "a five-legged sheep,"  and unsurprisingly, such a thing doesn’t exist in the real world.
The metaphor is used to describe something that is extremely rare, almost impossible to find, highly unusual or unrealistic.
You’d use this phrase when talking about a person, object, or situation that is so exceptional, unique, or rare that it’s nearly mythical.  Like finding a unicorn.

Origin

Unsurprisingly, the phrase comes from a humorous and ironic image - not from some ancient scroll about sheep Olympic tryouts. It probably popped up a couple of centuries ago in the world of folk humor or rural storytelling, where people loved to invent absurd creatures to describe things as rare as a polite mosquito that skips your blood type.

Now, a sheep is your average, everyday fluffball; the kind of animal that probably just wants to nap and chew grass. But add a fifth leg? Suddenly, it’s the unicorn of farmyards: bizarre, unnatural, and about as likely to stroll into your local café as a flying pig  - which is exactly why it stuck around.

So over time, this goofy idea became the perfect way to describe anything super rare or practically impossible, like landing a dream job without needing two decadesof experience, or spotting a “once-in-a-lifetime” deal that’s probably just a scam from your internet browser’s dark corner.

Examples

Ce candidat est parfait : bilingue, expert en informatique, flexible… C’est un vrai mouton à cinq pattes !
This candidate is perfect: bilingual, an IT expert, flexible… A real five-legged sheep!

Ils cherchent un appartement en plein Paris avec six chambres, un jardin, et un loyer bas… un mouton à cinq pattes.
They’re looking for an apartment in central Paris with six  bedrooms, a garden, and low rent… a five-legged sheep.