It took Jack a good minute to realize he was awake. Another two before he figured out why: there was a faint line of light coming from under the bathroom door. The bathroom adjoining his and Hiccup's bedrooms.

Knowing he couldn't in good conscience go back to sleep with his twin unable to do the same, Jack kicked his covers off with a whine. The ruggs on his floor were colder on his feet than the bedding had been. He wasn't looking forward to the frigid bathroom tile, but Rapunzel slept with her door open right across the hall and he could only deal with one sibling in the middle of the night.

Hiccup halted his frantic pacing when Jack grumpily hopscotched into the carpet, one hand halfway through his disheveled hair. After closing the bathroom door behind him, Jack expertly maneuvered his way through the scattered books and papers littering the floor to Hiccup's rumpled bed. He crawled into the mess of blankets and tucked himself in. Hiccup watched him somewhat hopefully. When he was all settled Jack waved a hand in the unwilling night owl's direction.

"Talk," he commanded. Hiccup instantly complied, launching into an explanation of some engineering snag one of his projects had hit.

Hiccup wasn't an insomniac. It was just that, sometimes his big brain found a problem or a theory or some random bit of information and got stuck, playing it in his head on repeat until he did something with it. But on nights like tonight there wasn't anything he could do with it, so it spun and spun around until it nearly drove him insane.

Jack had found about a year ago that sometimes all Hiccup needed was an actual person to talk to, rather than himself or the blueprints and diagrams and other drawings on the walls. Most times he only needed to run a problem out loud or share a train of thought and his brain would decide that was good enough and let him conk out. Other times, and it looked like tonight might be one of them, Jack stayed up with him for hours or even through the morning.

Once, the routine had lasted for several days in a row. The two of them had trudged through school with sagging shoulders and drooping eyelids. But where Jack had slept through at least one class a day, Hiccup hadn't managed a wink.

Jack knew some people envied his brother's brain, the way he absorbed information and remembered everything and was always creating. The way it all seemed so easy for him. But at two in the morning, watching him pace a worn line in the floor, hair wild from repeated tugging, eyes wide and bloodshot, Jack was perfectly happy to leave the geniusing to Hiccup, feeling quite fortunate that a brain that active and intense was one of the few things they didn't share.

Jack bit back a sigh, tried to follow the engineering jargon spewing from Hiccup's mouth, and steeled himself for a long night.