Bon Dieu de bois

This being an expression which turned up in a translation into French of the Agatha Christie story 'Towards Zero', one of those stories into which the English television people have injected the otherwise absent Miss. Marple.

As far as I can make out, it is no more than a mild expletive of surprise, much the same as our own rather dated 'Good Lord' or 'Good God'. Or, according to the Spaniards: 'es una interyección que expresa admiración o sorpresa', which looks like much the same thing.

There is a variant 'bon Dieu de bois de saperlotte'. Littré does not allow this last word at all, although Larousse goes so far as to say that 'saperlipopette' is a working class expletive, without further explanation. Maybe a bigger Larousse would go the distance.

But while there are lots of such expressions combining the ideas of God, Christ, and blood, where one can see a connection, thoroughly documented in Frazer's 'Golden Bough', I am not seeing any connection here.

Bing turns up an association with the base wood of the cross to which the Christ was nailed. But this does not seem to fit.

Then there is the Bois du Grand Bon Dieu, just south of Thuin, on the Sambre in Belgium. A nature preserve well known to walkers and such like. Gmaps 50.333171, 4.291933. But again, this does not seem to fit.

Any thoughts welcome.