I've mentioned before that S's 'conversations' with imaginary 'friends' often make some kind of sense though they also contain a high proportion of nonsense words.
Then, every so often, from a stream of nonsense or half-sense pops a fluent and pretty complex sentence:
'Sorry love, it's not your fault but I would have liked to have done it.' (NB the use of the conditional perfect and present perfect tenses - I think!)
Extraordinary in its way. And this kind of thing is not uncommon.