Anyone know what was said at breakfast about 'a mass'?

Perhaps it is in a way. The priest must surely have known the chances of his mass having a congregation of any size is practically nil with a huge foreign army encroaching on his town and an enormous battle inevitable yet he still goes ahead with what he has been taught to do. In the same way, Britain and her allies will stand firm no matter what the odds are like and no matter Napoleon throws at them and fight to the bitter end however big Napoleon's armies are.

I think just after the line "Well he won't have much of a congregation" Napoleon makes the connection between the stubborn priest and the armies of the alliance massed against him and realizes it's gong to be a difficult day.

This is just what I think and all of it is pure speculation.

Umm, I seriously doubt it was Bondarchuk's intention to have Napoleon slap the table in frustration and storm out of the room so he could pass wind in private. What a hysterical scene that would be, the emperor himself unleashing an 'imperial wind' in the next room... lol!

The reason why Napoleon got upset and stormed out of breakfast table is sort of obvious. It had nothing to do with the defiant priest at Plancenoit and everything to do with the gloomy implications of Napoleon's wisecrack about the priest's 'congregation'. Napoleon was seriously concerned about the battle ahead. It rained terribly the day and night before the battle and the ground at Waterloo was positively soaked (the French wasted several hours waiting for the ground to dry and harden sufficiently enough to allow the movement of cannon from the roads to the ground). To make things worse Napoleon had no clear idea where the Prussians were or how effectively Grouchy and his sizeable detachment (nearly 1/3 of Napoleon's army) would be in preventing them from reaching the Waterloo battlefield. Take note what Napoleon was doing in the next room, he was sitting in the window, deep in thought with a map draped over his lap. Clearly his appetite was ruined by his worries. There too many unknown variables working against Napoleon before the first shot was fired... and he knew it.

Furthermore Napoleon was suffering from 'piles' or hemorrhoids, a condition which made riding a horse a particularly painful ordeal. I also believe he was suffering from some gastrointestinal malady which didn't help matters.