Phrase translation: 何を言い出すかと思えば

Question

I'm hoping to confirm (or receive corrections) on a guess I have about the meaning of a sentence.

I'm reading a manga, and Character A stares at Character B for a long time with a serious expression. Finally, she says:

Character A: ペプシコーラとコカ・コーラどっちがいいかな.

Character B: 何を言い出すかと思えば.

Character B's response leads me to believe that he's saying something like, "With a serious face like that, I had no idea what you were going to say." But I'm not sure if I'm correct. As far as I know, 言い出す means to "blurt something out", but the grammar here is confusing me. Would appreciate anyone being able to break this down for me, thank you!

Answer 1

Character A: 「ペプシコーラとコカ・コーラどっちがいいかな。」

Character B: 「[何]{なに}を[言]{い}い[出]{だ}すかと[思]{おも}えば・・」

B's line is basically an unfinished sentence that ends in the conditional 「思えば」. To understand this, you need to be able to finish the sentence yourself. (I am sure you have heard an explanation like this before.)

First, we know how goofy A's line sounds, don't we? It was not something B had expected A to say in the given situation, was it? That is when we reply with an expression like 「何を言い出すかと思えば・・」、「何を言うかと思ったら・・」, etc.

What is left unuttered after that "conditional" clause would be along the lines of:

「そんなことか！」,

「そんなどうでもいいことか！」, etc.

「そんなこと」 here , of course, refers to A's nonsensical line "Which should I get, a Pepsi or Coke?"

Unfinished sentences are so common in spoken Japanese that we do not even think they are unfinished. We do not really "intentionally" omit phrases; it is just how Japanese has been spoken. Even small kids use these if anyone is wondering.

It is not easy translating 「何を言い出すかと思えば」 as it is only a clause. To go as literal as possible, how about something like:

"Just when I was wondering what (good things) you might say!"

What is implied here is that B had expected a much more meaningful comment/statement from A.