A messenger makes use of an idiom when describing Jocasta's suicide to the crowd outside the palace:
Oh how she wept, mourning the marriage-bed
where she let loose that double brood—monsters—
husband by her husband, children by her child.
And then—
but how she died is more than I can say.
It is worth noting that the above quotation is a translation by Fagle, and thus whether or not the apparent idiom is a direct translation of the Greek or merely an approximation of the original Greek's meaning is hard to say. However, "but how she died is more than I can say" appears to be a version of the many classic English idioms that communicate some version of being speechless: "I am speechless," "I couldn't begin to explain," etc. The idiom conveys the notion of being unable to speak because a situation is so surprising, overwhelming, or (as is the case with Jocasta's suicide) horrifying that there are no words to describe it, although in actuality one could always describe it further.
The fact that the Chorus discusses how Jocasta died shortly thereafter confirms that the saying was figurative and not literal. The idiom emphasizes the sheer misery and horror of the play's climax, which is so terrible that it is almost too much to describe. By making use of figurative language, Sophocles is able to deftly illustrate the situation that occurs offstage.