Murmurer

I sat in Brookes Market to eat my lunch, sharing a bench with another bloke. A woman came and sat between us. She had some food in a box - some little sausage-shaped things. They must have been good, because every time she ate one, she murmured "Mmm, mmm!". She finished eating and looked at something amusing on facebook on her phone, and murmured "Hmm hmm!" I wondered if she knew we could hear her. Was I supposed to reply? Then she left.