The French title "Les Petits Mouchoirs" refers to an idiomatic expression that is similar to the English term "Sweeping something under the rug". You cover something up with a napkin or a handkerchief and pretend it's no longer there even though everyone knows it is. The English term "Little White Lies" is a similar if not identical concept.
The film was France's highest-grossing film in 2010, with more than 5 million tickets sold.
To get the cast used to each other - and to convey a lifetime of friendship - they all lived together for 3 days in the house used in the film.
After seeing Ne le dis à personne (2006), Jean Dujardin called Guillaume Canet and told him he really wanted to be part of his next film. Canet - a lifelong friend of Dujardin - was delighted even though the part he had in mind for him was actually a very small one.
The movie that Eric and Marie are watching is Scarecrow (1973), with Al Pacino and Gene Hackman.