Bilbo wasn't entirely sure when it started. Perhaps when Dwalin had appeared so unexpectedly at his door and then proceeded to eat Bilbo's whole supper. The dwarrow had stricken an extremely intimidating figure, axes at his back, tattoos trailing over his arms as he bowed, putting himself at Bilbo’s service. And then how viciously he had bolted down the crispy fish, caressing the lip of the of cup of mild mead as he stared at Bilbo like he was the next course in the meal. Or maybe it was the peculiar look of knowing that Balin had thrown at his brother when he sat at the table and ordered a spot of supper.
It might have started when Thorin had disentangled himself from Bifur, Bofur, and Bombur after Bilbo had accidentally strewn them all over his welcome mat. The beautiful dwarrow had risen with rather a lot of grace for someone who had just fallen through a door, and fixed Bilbo with his moonlight blue eyes full of venom, pointedly not placing himself at Bilbo’s service.
Poor Bilbo apologized himself breathless, and eventually, Thorin acquiesced to look shrewd rather than stern. Though, that may have had to do with the wolfish look that he exchanged with Dwalin, more than the hobbit's desperate pleas for forgiveness.
Indeed, the sweet music the Company had played had enchanted Bilbo entirely out of his wits, and the bone-rattling song had nestled itself deep in his breast. Their music had bewitched him, but the glittering of his unexpected guests’ eyes in the dark parlour had intrigued him greatly. He had heard tell of the Dwarrow having incredible eyesight in the dark, but this? Their eyes seemed to glow like a cat’s when they catch the light at night. And it seemed that Dwalin's gleaming eyes lingered on Bilbo.
Or perhaps it had started when had come scampering up to the Green Dragon Inn, desperate to catch the rowdy group before they left him behind. He had been in such a rush to catch his soon-to-be-companions that he had come dreadfully unprepared, a fact that he mentioned (and Gandalf, bless the old coot, had at least partially amended). Though he had asked to turn back, Dwalin had offered him his own hood, to keep the sun off of poor Bilbo's neck, and smiled mysteriously when the garment rather overwhelmed the hobbit's frame.
While Thorin had remained aloof, the other dwarrow had become fast friends. Affectionate, and talkative, they always disappeared whenever Dwalin slowed his pony to step beside Bilbo. While they talked of anything and everything, the warrior's gaze settled on Bilbo’s skin like a physical touch, sometimes so intimately that the poor little hobbit found himself brilliantly scarlet in the cheeks.
But whenever it had started, it truly began when they reached Rivendell.