"The guards can't see us."
English speakers pronounce glottal stops all the time and don't even realize it. If you start a sentence with the word apples, as in Apples taste good, you'll put a glottal stop at the beginning of apples. You almost can't help it.
Some languages in the world do not pronounce glottal stops at the beginnings of words unless they are put there intentionally. English speakers usually can't hear the difference.
In Klingon, no syllable may begin with a vowel sound. Since the glottal stop is a consonant, this is okay. The first letter — that is, sound — of 'avwI'pu' is ', a consonant.