All cats know this rule. And have better manners than most humans.
I do not wash when I am in doubt. In fact I wash when there is very little doubt.
But I would suggest that, when one is in doub*t, one should go out and buy something pretty to eat. It doesn't have to be a chocolate bar, though that can be very pretty; or a paper cone of French fries soaked in malt vinegar, prettier still, to my mind; it could be some courgette flowers. Or black raspberries. Or a bunch of Swiss chard. Or a lamb chop. Some brown eggs. And take whatever it is home and make something out of it.
The doubt will shift and one's focus will too, and soon there is the prospect of sauteed chard leaves with anchovy butter and lemon for dinner. Or courgette flowers tossed with some pasta and butter parmesan and...lemon. Or jam (with some lemon to help it set!). Or just raspberries with some brown sugar in a bowl, as much as you like, for supper.
Of course, exceptional medicine for doubt is champagne. You have a glassful, stick the rest in the fridge with a silver spoon down its throat, and have it for three more nights. Bubbles after a long day. The aura of it goes a long way. And it's not as much of a splurge as one thinks.
Now if only my jam would set.
[*ED. Footnote: said doubt related in no way to Canadian Frenchmen, and in some ways to work, domicile (continents, and the ills that beset them) and hormones. The jam turned out fine].