In reference to Nicola's sudden change of mood when Frank asked her about the summer solstice, I have just remembered my own experience of someone getting inexplicably angry at something harmless I had said.
I was on a group coach tour in Turkey. One of our party was telling us about the house she had recently bought upon her retirement. She mentioned that the master bedroom had an ensuite bathroom. Now, this must have been the late 1980s and I had at that time never come across a UK home with an ensuite bathroom for a bedroom. I associated ensuite bathrooms with hotels.
I said something amicably, normally conversational like, 'Oh lucky you, I have never heard of that before.' She suddenly glared at me and said, 'Well it's perfectly normal nowadays!' in a really angry voice, as if my comment had been offensive. She could have said calmly, 'It's becoming more common in new-builds' or something but instead was furious, possibly at my ignorance? But I didn't move in such circles.
Another case of unprovoked anger. The point I am trying to make (I do have one!) is that perhaps Nicola just went off on one for no good reason.