The subjunctive mood is typically used in such a way that the verb's meaning relates to how the speaker feels about it,in this case, It expresses how a person feels about a possible action or state of being and as a matter of fact this expression "me quede mudo" is not literally,usually is used by native speakers to express how surprising a thing might be. for example: --cuando supe que habia ganado la loteria, me quede mudo. --when I knew I had won the lottery, I was so surprised.( so suprised that I did not what to say)

If it's subjunctive, I would expect something before it, like "Él está alegre que..." However, when I lived in the US city of Worcester, the free Spanish language newspaper there was *really* bad about putting in the accents. So what you might have is, "me quedé mudo" without the accent.

Porque quedé es pasado y quedo es presente. Me quedé mudo - pasado - "Cuando me besó, quedé mudo". Me quedo mudo - presente - "Me quedo mudo cuando veo un fantasma".

你学西班牙语多长时间了 啊

Quedo se usa cuando se habla de otra persona, "el, ella" y quede cuando se habla de si mismo "yo" La conjugación seria Yo quede Él quedó Ella quedó Espero haberte ayudado n_n