Spent most of today giving my Austin a full Spring clean, I guess thats what sunny weather makes you do! Removed the back seat and found my cleaning cloth in shreds, yes you guessed it, an univited passeger had made an nest and was hibernating. Felt a little unhappy to find it was a dead field mouse, most likely died of shock as I have used the car recently.
Have you checked the little corners and crevises in your car recently?

Funny you should mention mice. I just went to fill the Cup Model up with water only to discover a dead mouse wedged into the end of the watering can, thus explaining why I could get no water from it.