No sé qué literally translates to "I don't know what", but it's a popular phrase used to describe a special, hard-to-define quality—the Spanish equivalent of the French je ne sais quoi.
In the song, the singer feels this indescribable spark when their hands touch for the first time: "Sentí ese no sé qué" (I felt that 'certain something'). It perfectly captures the mysterious feeling of instant attraction, making it a charming and useful phrase to learn.
Have you ever met someone and instantly knew you had to take a shot, even if the odds seemed terrible? That is the exact rush Becky G and Paulo Londra bring in "Cuando Te Besé". The song kicks off with Becky admitting her first thought was "Supe que no eras para mí / Seguro tenías a alguien" ["I knew you weren't for me / Surely you had someone"]. But curiosity won out. A simple street walk and a sudden hand squeeze sparked that mysterious "no sé qué" ["I don't know what" - an indescribable spark], leading straight into a life-changing kiss where she felt she "toqué el cielo" ["touched the sky"].
Paulo steps in and flips his whole attitude upside down. He literally calls himself "Forever alone" [a nod to the internet meme for chronic bachelors] until he spots her. Suddenly, being solo is out the window, and all he cares about is dancing: "No te vayas que se apaga mi ilusión" ["Don't leave or my dream will fade"]. The whole track is a fun, back-and-forth confession about that one magical kiss you would repeat "de nuevo, y de nuevo, y de nuevo" ["again, and again, and again"].