[X] Stay still, just let the guards look the cart over and don't antagonize them. They aren't looking where the master sword is for now.
Problem with trying to talk is they may look at us, which risks them catching the sword, and tripping them up will piss off the captain who will probably try to take his embarrassment out on Malon and her cart. Yes, something will undoubtedly go wrong no matter what we choose, but I'm aiming for playing dumb.