Wondering about the origin of the expression "Ouistiti"? And, the use of the expresson " Souriez" for "Say cheese" ?

Question

Well, so it's true: You do learn something new every day! And for me, it's the expression, "Ouistiti" !

I had looked up "Say cheese", (in both Collins and the Larousse), and found only "Souriez" !

I wrote "Souriez", which was marked wrong. Maybe, I should have written, "Souris" ! the second person imperative, instead of the formal/plural imperative?

Even when I search 'ouistiti' I can only find that it means 'marmoset', ("un petit singe arboricole d'Amerique tropicale et aux fortes griffes") Also that the expression, "Un drole de ouistiti" means " a bit of a weirdo" ("une personne bizarre"). Does anyone know the origin of the expression, "Ouistiti"?

Merci a tous et bonne continuation !

Accepted Answer

Hilary,
 I would guess that it is because pronouncing ‘ ouistiti ‘ is ‘ teeth-displaying ‘ as is pronouncing ‘ cheese ‘. It probably doesn’t hurt that both words have meanings that are otherwise quite out of place in the situation. 
Interestingly, having just been in France, taking and being in souvenir photos, ‘ cheese ‘ was understood and used by French native speakers across a wide range of ages, and not once did I hear ‘ ouistiti ‘. Whether our French friends/family were using it because I was there, or would have anyway, I can’t say !
https://www.wordreference.com/enfr/cheese

Answer

Hi Hillary!  I use WordReference which has ouistiti also as an interjection meaning cheese.  They give the following example:  Le photographe nous a demandé de dire « ouistiti ! »