Ratso has had the bad taste to die before the exterminator could get him. Exterminator came Wednesday. Thursday morning the unmistakable odour of dead rodent was coming up the back air shaft. Far too fast for a beast that I was assured would take days to take the bait, being the wily critter it is. Have blocked up the vents between bathroom and study and thanked providence for warm weather that lets me keep windows open. I can still smell the acrid tang, but then I'm me. A few more days, judging by the Little Girls' experience with two successive gerbils that escaped into their air duct.
And bought a ceramic heating fan for Sunday, when the temps drop to 5 overnight, if the smell isn't gone by then.