Puñales literally translates to "daggers". It's a dramatic and powerful word that you don't often hear in everyday conversation, making it very memorable.
In the song's iconic opening line, "Flaca, no me claves tus puñales por la espalda" (Skinny girl, don't stab your daggers in my back), Calamaro uses this word as a potent metaphor for betrayal. It creates a vivid image of being hurt deeply by someone you trust, setting the emotional and dramatic tone for the entire song.
This song starts with one of the great opening lines. The singer tells a woman, "Flaca / No me claves / Tus puñales / Por la espalda" (Skinny girl, don't stick your daggers in my back). But then he immediately follows this dramatic accusation with a cool, almost unbelievable claim: they don't hurt him. He says that deep down, "Las raíces / Del amor" (the roots of love) will stay where they always were, buried in the center of the earth. The song lives in this conflict between a bitter breakup and a love that he feels is too fundamental to be destroyed.
He remembers their shared past, their "abriles olvidados" (forgotten Aprils), which he's left in the back of a closet. The song's most famous part is a list of impossible demands he makes of her: "No me mientas / No me digas la verdad" (Don't lie to me, don't tell me the truth). He doesn't want lies, but he can't handle the truth either. He admits his own faults too, confessing he's been like a "perro ideal que aprendió a nadar / Y a volver al hogar / Para poder comer" (an ideal dog that learned to swim and come home to eat). It's a complicated, messy, and very honest look at the end of a relationship.