Sans is a MONSTER and not a HUMAN, so he doesn't follow HUMAN biology like a HUMAN skeleton. Same with Gaster and Papyrus.  

Author note: Sorry if this bit is a bit short. Originally wrote it a few days ago but then accidentally deleted like half of it when trying to copy it over to Wattpad on my phone and I had to rewrite it.
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They had beautiful weather out here, on their honeymoon. The sky, was almost a clear, silky blue, with the exception of a couple of dancing, floating clouds, that looked like small groups of cotton wool all bunched together. Sunlight was beating down onto the deck of the ship, heating it up to the point that you would probably be able to slightly feel the blazing heat through the bottom of your holiday sandals, (if you chose to wear any of course). It was quite hot, but thankfully that wasn't made too painful, by the nice, cool breeze, that would sweep in every now and then, bringing pure comfort to anyone who might have been concerned they'd pass out, due to the sun's rays.

Frisk was leaning her arms upon the railing of the deck, allowing herself to enjoy the feeling of the wind swirling through her hair, and through the light flowy, sleeveless, light blue top she decided to wear. She also chose to wear a light blue hat to go with that top, alongside a pair of denim shorts. Lastly, she was wearing a pair of sandals upon her two feet.

When she decided to step away from the railing, it wasn't difficult to find her skeleton husband, dressed in a dark blue, buttoned up shirt, with patterns of palm leaves upon it, that were in a lighter shade of blue. His shorts were just plain black, while he was also wearing his own pair of sandals. She also couldn't miss the fact that he had a pair of shades, stuck to his skull, as he was resting his arms behind his head; he was relaxing on one of the many sunbeds they had upon the deck. With a giggle, Frisk decided to make her way over to the free sunbed that was next to his, and went to lie across it with a relaxed sigh. "Hoping to get a tan, are we?" She teased.

"as if." Sans joked back in a sarcastic manor. He was all bone, in no way could he get a tan. Of course he knew his wife was only teasing. His wife... It was still so new to him to think that, that Frisk was actually his wife. Not his girlfriend, not his fiancée: his wife. Crazy. Crazy, in the best kind of way. The kind of way where it just made you want to keep smiling all day long, because you couldn't stop thinking about how happy you were about it. "seems like we picked a good time though to come out here."

"Definitely." Frisk agreed with a small nod, going to grab her own pair of sunglasses that had been latched onto the neck of her top. Good thing she brought them, otherwise she might have been squinting a lot on this trip whenever they decided to step foot outside. "I wonder how everyone at home is doing..." Frisk sighed, relaxing her head against the sunbed she was lying upon. Sans chuckled.

"i'm sure they're all fine. especially leo and luna. probably havin' a blast with papyrus as we speak." Sans grinned towards Frisk, staring at her through his sunglasses. He couldn't blame her for thinking about everyone though and how they were doing. He was doing it too, while trying not to show it. But this should be their time to relax. Not think about anything that might have been going on at home.

"Yeah, that's true." Frisk said. Papyrus was a great uncle-- Mettaton was great with the kids too. Together, they made a very good team when it came to looking after Leo and Luna. The human wouldn't be surprised if they decided to have kids of their own someday. They would be amazing parents. "It's still hard to believe that we're here though; that were actually married." Frisk beamed, as she began lightly fiddling with the wedding ring, that rested on her left hand. It was still hard to get over that it actually happened. Not even just because it was with Sans, (and their relationship had a rocky start), but just because she never thought she would be so lucky.

"Don't you agree?" Frisk wondered, only to raise her eyebrows a little towards her husband in wonder, as she couldn't help but notice the fact that he was suddenly sitting up, glancing further down the deck, and he even went ahead to remove the shades he was wearing. He looked almost thoughtful. Confused. Maybe a hint of concern? "Sans?" She spoke up. He didn't answer. "Sans, are you okay? What's wrong?"

"uh... it's probably nothin'. might just be my mind playin' tricks on me." Sans murmured, but the human wasn't so sure if he was even trying to convince her. Maybe he was trying to convince himself instead.

"No, come on. It's clearly something." Frisk frowned. She had the feeling he was just trying not to concern her, because they were on their honeymoon, and there should be no reason for them to stress about anything. Not about their family, friends, or even the Mafia. They should be able to be out in their own little world right now. Would that continue to be the case though?

"well call me crazy, but i could have sworn i saw andrew?" Sans stated, which only caused Frisk's own expression to change into a look of bewilderment. Andrew? Why would he be here? And if he was here, there would have been no reason for him not to say hi. He wasn't afraid of Sans anymore, in fact the two were on pretty friendly terms now; had been for a little while. So... What if...?

"I don't think it's Andrew." Frisk stated. "Don't you remember? A long time ago, when you first met Andrew, in... Not very good circumstances..." Frisk weakly chuckled at the thought. "He mentioned his brother. That he had a twin. Wasn't it... James?" Which was originally the alias that Andrew had gone by. He wanted to make his family happy with him, he said. Even though he didn't agree with his family, he had just wanted them to be proud of him.

"why would he be here though? why now? to tell the truth i woulda thought he'd be dead." Sans admitted with a small shrug of the shoulders. It did make the two of them slightly nervous admittedly. Because if anything went down, well, they were in the middle of the ocean. The middle of nowhere. Asking for help from the others might be somewhat difficult, right? "i'd watch out for him. maybe he's just been waitin' for a good time to get us back."

"Maybe." Frisk agreed with a small nod. She glanced back in the direction Sans had been staring in, only to see that the supposed sighting of James was nowhere to be seen. He probably left and went inside after Sans had spotted him. Great. They had to deal with him while on their honeymoon... Well, it was best to try and not let him ruin it. They could still have a good time, before it would possibly get ruined by her friend's brother. How could two people be in one family together yet be so crazily different? One wanted good things, the other, bad. She may never understand it, but at least Andrew was safe from his family.

Maybe that's what James wanted. To take his brother back. Either to force him to do evil deeds, or maybe they wanted to hurt him. She didn't know. But they would keep Andrew safe. They'd keep everyone safe from James.

But for now they should just enjoy their honeymoon.