The end of World War I in late 1918 permitted European artists to return home gradually, and American artists to travel abroad. Dada's arrival in Paris in early 1920 brought together many artists who had been active elsewhere, including Arp, Ernst, Duchamp, Picabia, Tzara, and Man Ray. These dadaists, and others already in Paris, burst onto the scene with a frenzy of activities including six group performances, two art exhibitions, and more than one dozen publications produced in a five-month span known as the "Dada season."
Duchamp brought the New York dadaists' fascination with commodity culture across the Atlantic to Paris and expanded his critique of the traditions of art. In one of his best-known works, he altered a reproduction of Leonardo da Vinci's Mona Lisa by adding a beard and moustache and the letters "L.H.O.O.Q." When the inscribed letters are read in French, they form the sentence "Elle a chaud au cul"—a vulgar phrase indicating the sitter's sexual availability. (When the letters are read as a single word in English, it approximates "Look.") With these "adjustments," the artist transformed one of the most famous portrait subjects of Western art into a tart with a cheap slogan. He also made a mockery of art history by construing the Mona Lisa as the punchline of an off-color joke. While Duchamp intended to make his audience laugh, his graffiti-like actions had an aggressive edge, a feature shared by much of Paris Dada. The American artist Man Ray, for example, affixed brass tacks to the bottom of an iron, converting an ordinary household object into a weapon.