James tries very hard not to betray his scepticism at Sparrow's words. Find a heading. James has never been a first mate aboard a ship himself, but he's commanded plenty, and he knows that generally finding a heading is the Captain's duty, possibly the navigator's, if it's a large ship and they have a navigator at all. But if Sparrow wants him to help find a heading, he surely can do that; perhaps find out more of what Sparrow wanted earlier with all his talk about England.

Furthermore, he is decidedly uncomfortable as to signing the articles of the ship. That puts him in full responsibility of anything he might do as a crewman of the Black Pearl, and that makes matters awkward for when he finally does return to Port Royal (for there was never a doubt in his mind that this is not a permanent state of affairs, and that eventually he'll resume his commision). There's no way, though, to refuse to sign the papers after he's just accepted the post of first mate, and he is not eager for another fight with Sparrow.

The food, however, he has no qualms about. All he's eaten today was that orange, and he had really hardly tasted it, given the... purpose for which he had been eating it. So he offers Sparrow a thin smile and says

'Indeed.'

He's about to offer to accompany Sparrow, but a look on the pirate's face suggests that he leave him be at least for the moment. He'll need to inform the crew, for one thing, that they've taken on the Scourge of Piracy as first mate, and quite honestly, James would rather not be present for that. Instead, he inclines his head in the direction of the door, a vague invitation for Sparrow to be on his way, and sits down at the table, pulling across to him the map they'd been examining earlier.