A "glottal" is a consonant that is pronounced in the back of the throat where the glottis is vibrated against the back of the tongue. Arabic and Hebrew have pretty heavy glottal consonants. Spanish speakers frequently use a light glottal touch -- what I called a "flip" -- with the aspirated "J/H" sound.
Sorry for the delayed answer -- I need to get back to Duo.
The Spanish "uno cosa grande" might be translated to English as "a big thing", but that does not mean that "un objecto grande" could not be translated that way, too. I understand if we were asked to give a literal translation. But, Duolingo often accepts translations which would commonly be spoken in English to mean the same thing. I believe, in this case, that many, many people in America would normally say "thing" instead of "object" and mean the exact same thing. It is a normal sentence. In fact, many people would be uncomfortable saying the word "object" in this sentence, feeling it was way too formal. So, I believe the translation "a big thing" should be accepted in this case.