So it turns out that whilst we were away at #EO2026 a pigeon apparently managed to get down the chimney and into the living room.
I think that it was unfortunately stuck in there all through the heat wave, and with the airco off and everything shut tight it got to 40 degrees inside as well.
No water, so it did not survive. And it did not go quietly into that good night. A lot a lot of things (carpet, furniture, shelves, lights) are covered in pigeon poo.