Exegesis:

kai autoi ou sunēkan ‘and they did not understand.’ autoi ‘they’ as contrasted with Jesus.

suniēmi ‘to understand,’ ‘to comprehend.’

Translation:

Did not understand, i.e. they were unable to grasp the full implications and real intent of the saying. Some versions use here a specific verb (e.g. Pampanga, a derivative verb the root of which means ‘to penetrate into the inner part’ and is cognate to a word for ‘sharp’); others employ the general verb ‘to know,’ but add to the object a word for ‘intent/(real) meaning’; cf. also, ‘but they did not know what his words … really meant (lit. the place to which his words … came-through)’ (Tboli, making use of an idiom said of people who do not know the answer to a riddle or the true meaning of an allegory).

The saying which he spoke to them, or simply, ‘what he told them,’ “this reply” (Phillips).

Quoted with permission from Reiling, J. and Swellengrebel, J.L. A Handbook on the Gospel of Luke. (UBS Handbook Series). New York: UBS, 1971. For this and other handbooks for translators see here . Make sure to also consult the Handbook on the Gospel of Mark for parallel or similar verses.