Claudia even had to invent a new percussion effect on the violin. I open with a kind of golpe where you slap the strings against the frets, an effect used in Latin American music. Later on, when the violin layers the same passage over the guitar, I wrote that it should be col legno or with the wood of the bow, a common effect, but in this case without pitch. That didn't really work so Claudia just started doing the same thing that I was: slapping the strings against the fingerboard. It is not quite as effective as the violin doesn't have frets to hit against, but it does match with the guitar better.
UPDATE: I forgot to say where the title comes from. Living in Mexico one often runs into words from Nahuatl, the language of the Aztecs. In fact, we even have a few of them in English: tomato, chocolate and coyote are all words from Nahuatl. So when I was writing the tango, I thought I would create a new word for the title. The Nahuatl prefix "xi-" (pronounced "she") creates a command or imperative form of the verb. So, "Xitango" is saying "dance tango!" It is also a trilingual pun: "she tangos".