"'You are Martin's father, are you not?' A woman beside Routh had turned to him and was looking at him in friendly interrogation.
"For a moment Routh stared at her in stupid panic. Then he nodded spasmodically, 'Yes,' he said, 'that's right. I'm Martin's father. ' ...
"'I saw the resemblance at once. May I introduce myself? I'm Elizabeth's mother.' The woman laughed charmingly, as if there was a great deal of merriment in this fact. ..."
Operation Pax, J I M Stewart, 1951.
I speculatively advance the thought that this usage ... the formulaic rhythmic conversational laugh ... is commoner among women that among men; and that it is an attempt to lighten a statement or observation that might otherwise seem overweighted ... or oversolemn ... or even pompous.
I hear it particularly often at bus-stops among nice old ladies ... exchanges such as:
Sunny day today, isn't it uc uc uc.
And a bit warmer than yesterday uc uc uc.
Bus nearly running on time today uc uc uc.
Not like last week uc uc uc.
Spect it was the building works on Folly Bridge uc uc uc.
Kai ta loipa ...