It's not much of a smile that Martin has to offer, small and exhausted, but it's better than nothing. Hell, that John managed to earn a smile by some other means than simply embarrassing himself is... sort of nice. To the extent that 'nice' can apply to his current situation, that is.

He gives Martin's next question a beat of consideration before shaking his head again. He's still too unsettled for the thought of food to have any appeal, and besides, what would Martin give him? The absence of actual cat food in his flat could probably be deemed a mercy, as the thought of eating that is appalling, but most of the human foods John could safely consume like this would require some preparation. He doesn't want to put Martin through the trouble of cooking him eggs at this hour.