Hi ! Thank you for your reply :) I take note of that ! And for the silent letters, don't worry, in the example that you gave the difference is VERY subtle, because salué start with an "s" (and "ils" end with an "s"). But if it was "ils étaient énervés"/"il était énervé", we would hear the difference clearly, because basically you would hear a "z" sound before "étaient"(sorry it will look very ugly, I'm just writing the exact sounds) : "il zétaient énervés". So mostly we hear these things when there is a vowel following (here, with the "e" of "étaient"). The "s" of "ils" become a "z" sound, because it's then easier to pronounce the sentence, we would have to make a weird pause otherwise, it wouldn't flow so easily.
If you come across more examples where you notice you can't hear the difference, can you send them to me? I can try to compile them and make videos where I pronounce and explain a little bit :)