Why do pears...

 ...suddenly appear turn to over-ripened mush when one is least expecting it?

 I was just downstairs wandering from room to room with the phone clamped to my ear chatting to being chatted at by Indescribable. She was going on about how she took Babyzilla to the shops yesterday afternoon and bought some praline & cream icecream and cranberry & orange cookies. She ate the icecream last night (but didn't really like it) and scoffed the cookies this morning for breakfast. 
 As she gabbled on, I looked around for sustenance as I had yet to break my own fast (having spent most of the morning in the bath). The only thing I could see of slight deliciousness were three conference pears on the kitchen windowsill that were given to us by The Father from his pear tree. They'd been there for the past two weeks in the hope that the meagre Autumn sun would ripen them.
 I gently squeezed each pear, choosing the last one as it had a little "give". While my sister was prattling on, I bit into it and nearly broke my teeth! How can it still have the consistency of granite? How? It should have turned to mush by now!

 Eddie Izzard has the same problem it seems:



 There's a longer, more comprehensive video here (the pear bit starts from 4:30).