I hear you knocking

A few minutes ago I heard knocking at our back door. The door isn't accessible to callers, it's half glazed and I could clearly see that there was nobody there. I was mystified and began to doubt myself. Did I really hear it? Then, there it was again. After a minute the mystery was solved, there on the door handle was a Great Tit and it was pecking at the glass. Then it ducked down and was obviously having a go at the wooden part of the door. It carried on for a while but flew off when I called Jacqui to come and see it. When I told her that there was a little bird knocking at the back door, I didn't like the way she smiled and said "yes dear"!