All David has to offer Franz is his tea, which he doesn't suppose the dog would like terribly much, and more petting, so he opts for the latter. He supposes if he had siblings, he might have all sorts of ideas about what sorts of mischievous things he could do to someone while they're asleep, but as it is, most of the pranks he knows involve drawing on faces, so he simply curls up a bit and watches Urquhart sleep for a bit. If he really starts snoring, David will wake him, for the good of the rest of the bar.