This bird is a bit confused as to its whereabouts. I was sitting in the living room with the back window open about six inches at the bottom. It suddenly flew straight in whizzing past my shoulder and settled among the house plants at the other end of the room.

 I opened the window to the fullest extent and eventually it returned to the great outdoors after exploring various nooks and crannies among the bookshelves and furniture. A baby Robin I think; fledglings take a while to develop the characteristic red breast plumage. 

 It wasn't particularly concerned by my presence. I'm glad Kate the cat wasn't in the room at the time or it would have been mayhem.