The black goat receives a letter from the white goat but she eats up the correspondence upon arrival. So she writes back: さっきの手紙のご用事なあに？(Sakki no tegami no go-yōji nāni? "What were the contents of your letter?"). Since the white goat is prone to the same eat-before-reading habit, the story in this Japanese children's song やぎさんゆうびん (yagi-san yūbin, "Goat Mail") goes on and on endlessly, with one of the two protagonists wondering anew each time about the 何 (nani, what) of that unread letter.

And even if you're no goat, nor any other kind of letter-muncher for that matter, there are, in fact, quite a few things to wonder about with 何.

To start with, the kanji has two slightly different readings, and these seem to make it mean substantially different things. The first one is nani (in the goat song, the "a" sound is stretched in the way children would say it), and it translates very straightforwardly as "what." You'll find it in inquiries such as 何がいい？ (Nani ga ii? "What would you like?"), 何がいけない？ (Nani ga ikenai? "What don't you like about it?"), or just plain 何？ (Nani? "What?"), which depending on intonation can be everything from a careful request for clarification to a strong expression of disbelief or contempt. Just like in English, basically.