This is something my grandfather would say when he saw something that caught his interest. He might say it when someone told a good joke, or even a bad joke – he was fond of jokes. He might say it as punctuation to your story. He might say it if he came upon you in a room, or around the bend or on the patio.I imagine he might have said it silently while reading the murder mysteries he loved, when the killer was revealed.
My grandfather was also a great fan of “a-ha!” and could be heard to say it interchangeably with “O ho.”
I was reported, as a small child, to have picked up this vocal tic and said it, too, on similar occasions, for a while – probably until I realized that everyone was laughing at a small girl saying a grandfather’s words.