It all started soon after 10 o'clock. First, a bluetit approached the box and hopped onto the entrance hole for a good look in.
The colder weather that we have had recently has removed any thoughts of nesting our birds may have had. They must have been concentrating on the even more basic business of surviving. The number of visits to our boxes has dropped significantly - on several days Box1 did not have a single visit.
Today was a bit brighter and two bluetits seemed to be playing around in and on Box1. What happens is not obvious even though we have both an inside and an outside camera watching the events! However, after extensive examination of these pictures, this is what I think happened.