Why do Spanish singers drop the "S" at the end of words?
I've been listening to a lot of Spanish songs (especially by the friggin' talented Alejandron Sanz) lately and I notice how they drop the "S" at the end of words like "pensamos", "historias" etc etc although sometimes they do pronounce it. I'm not sure when to drop it and when to pronounce it. Is there like a rule or the "S" is just optional?