The speed of sniff

Yestereve I cooked the Xmas ham - or the first of the Xmas hams, if I end up giving it all away as I usually do. I boiled it (well, barely-simmered it), glazed it, cooled it, covered it and put it in the fridge.

This lunchtime? Ham for lunch. Obviously. So I took it out of the fridge.

Before I had put it on the counter, before the fridge door had swung shut again with its particular thunky sound, I heard:

the thump above my head, that means Barry had been having a drink from the tap in the bathroom basin and has now jumped to ground again;

the desperate thunder that means Barry is racing hectically down all the stairs in the house;

the pitiful mew that means "Hullo, I'm here now, and I really need ham."

This is before I've uncovered it, surely - despite the title to this post - before molecules of hammy-smell have had time to rise to the bathroom.

How the hell did he know?