I have two rescue cats (not from the same litter), Stan and Bunty and they both get on very well. But while Stan is very friendly all the time, Bunty shrinks away from me during the day. I go to gently pet her and she dodges away. Anyone seeing me with her would think I spend my time shouting at her as she looks at me all wide-eyed and wary. She's five now and has always been like this. She doesn't mind Stan washing her though and quite often I find them curled up together.
But at night, Bunty is completely different! I put a blanket next to my pillow and Bunty will sneak in next to me, curl up and go to sleep. If I wake up and pet her she actually purrs. And before you say, it's the blanket, she does often sit and sleep on it during the day but if I pet her during the day she shrinks away from me!
I think she's got an identi-cat hidden in the attic. 'The Picture of Bunty Grey'.
