I was wondering how an emphasis would change with a word of only two letters. I'm trying to say it according to your note, and finding it hard to make it feel right in my mouth, but I don't know a whole lot about the sound of Portugese on the whole. Is the "s" sound always pronounced with that "shh" feeling to it, and how does it differ from the "sh" sound in English? Sorry to keep asking all these questions, I'm just curious.
It's like in Polish, where "sz" is pronounced more or less like the English "sh", but there's another sound, an "s" with a little accent mark over it, which is pronounced similarly, but with the tongue a little more relaxed, and the air going over the top of it rather than more along the front. English speakers always seem to have a hard time even differentiating between the sounds, though, to say nothing of trying to duplicate them. I wonder if this is something similar?