S's 'conversations' now contain many more made up words and sounds than they used to. But you still hear 'proper' word, phrases and sentences mixed in with the made up stuff and, if you ignore the words/sounds (which is difficult) the ebb and flow of 'proper conversation' are very evident.
The other day I 'tuned in' at a point when S had stopped for a bit and was 'listening' to the other person in the conversation. Then I heard a chuckle and 'I knew you were going to say that!'
I'm sure that, before dementia struck, S would also have found this amusing.