Bran I, ACOK: They didn't have to tell the truth, but the oaths were binding unless they said "Mayhaps," so the trick was to say "Mayhaps" so the lord of the crossing didn't notice. Then you could try and knock the lord into the water and you got to be lord of the crossing, but only if you'd said "Mayhaps." Otherwise you were out of the game.
Cat VI, ASOS: "My lord!" Catelyn had almost forgotten. "Some food would be most welcome. We have ridden many leagues in the rain." Walder Frey's mouth moved in and out. "Food, heh. A loaf of bread, a bite of cheese, mayhaps a sausage."