It was, Astrid knew, one of the things she loved most about him. It was also one of the things that had taken her the longest to appreciate.

The first time she noticed it, it had worried her.

She remembered the moment clearly. She and Hiccup had been sitting together at a cliff's edge, shoulders touching, their backs against Toothless. And as with any dragon, she could feel the heat radiating from Toothless at her back. But she frowned suddenly as she realized she could feel heat radiating from Hiccup, too, albeit less intense. She turned to him, frowning still, and leaned away a little to get a better look at him. Feeling her movements, Hiccup turned to look at her, his confusion evident in his emerald green eyes.

"Uh… Astrid?" he asked confusedly, squirming under her intense gaze. "Uh, what… what are you staring at?" Astrid didn't respond, but purposefully moved a hand toward his forehead. He ducked away nervously.

"Hold still," Astrid told him sternly, and he reluctantly complied. She felt his forehead, and her frown deepened. "I think you have a fever, Hiccup," she said seriously.

"What?" he asked, eyes widening in surprise. But before Astrid could say anything more, she saw his eyes light up in understanding. "Oh!" he exclaimed. "No, no, no," he placated, smiling in relief and reassurance. "I'm fine, Astrid," he said. "I'm always this hot." Astrid couldn't help the little laugh that escaped her at that, and Hiccup immediately reddened. "Oh, no. Oh, I don't mean that kind of hot. I mean hot hot. Like, not figuratively. Oh, gods," he mumbled, and he buried his head in his hands in embarrassment. A second later, his head shot back up again. "How about a flight?" he asked breathlessly. It was his go-to way to change the subject, and Astrid could see why; it always worked. They had jumped on their respective dragons, and any and all of Astrid's thoughts or worries had flown away with the wind.

The second time she noticed it, it had perplexed her.

It had been during a lesson at the academy, when Hiccup was touting the importance of constant and unbroken trust between dragon and rider. While Snotlout grumbled something about it being easy for Hiccup to say, having jumped off a cliff for his dragon, Hiccup ignored him and reminded them of the trust they had had to place in their dragons in the beginning. As a demonstration, he had grabbed Astrid's hand and placed it atop Stormfly's snout.

"Remember that feeling?" he asked quietly, and his voice was reverent, as if he were remembering that moment himself. Astrid knew she was supposed to be paying attention to her dragon, but with Hiccup's hand still lingering over hers, she felt the warmth of it, and was distracted. Why was he so warm? But, lost in her thoughts, she hadn't realized she was staring at Hiccup instead of Stormfly. That is, until Snotlout laughed teasingly, and opened his mouth to make a comment. Of course, being Astrid, she had shoved him to the ground in one swift, fluid motion, so that the only thing he had ended up saying was "ow".

The third time she noticed it, she finally appreciated it.

She was walking through the village with Hiccup, headed for the great hall, their dragons trailing behind them, playful in the winter snow. A forceful wind blew out of nowhere, and Astrid steadied Hiccup as he nearly fell over.

"Thanks," he grinned sheepishly. She grinned back, and as another gust of wind blew around them, she couldn't suppress a shudder. She saw Hiccup's emerald eyes flick quickly over her, a studying glance.

"Cold?" he asked her, taking in her scrunched posture and occasional shiver.

"A little," she admitted. And Hiccup, having no jacket to give her, simply moved closer and wrapped an arm around her, rubbing a hand briskly up and down her arm. She felt instantly warmer, as if he were a great fur coat, or a dragon himself. She looked at him in slight surprise.

"Better?" he asked her. She nodded, preoccupied with her thoughts. Why was he so warm all the time? She looked down at the hand that was currently rubbing her shoulder. The movement pulled his sleeve up a couple inches, and she saw an old burn mark on his forearm, one of many, thanks to his time working in the forge. And immediately, the answer hit her like lightning, making her feel foolish. Of course he was warm; he had spent nearly all his life next to the blazing fires of the forge, and now, he was in constant contact with at least one dragon at all times. As she realized this, another harsh wind shoved them roughly, knocking Hiccup over and taking her with him. And as if to prove Astrid's point, Toothless immediately materialized next to Hiccup with a concerned and questioning warble.

"I'm fine, bud," Hiccup assured Toothless with a soft laugh, and he righted himself with his dragon's help. He offered Astrid a hand. She took it, relishing the warmth as she stood. Then she punched him on the shoulder.

"Ow!" he complained, frowning, but his green eyes were dancing.

"That's for knocking me over," she told him sternly. And then she pulled him close, pressed her lips to his.

"And that's for keeping me warm."