It had taken quite a bit of convincing. Celestia and Luna were with her this time. Twilight was the one doing the study itself. The three of them had taken every precaution. They weren’t sure how magic would work inside a dragon. On the trip to the dragon lands, by train most of the way, the three Alicorns cast powerful reformation spells. Twilight sat in the middle of a small circle while Luna and Celestia sat behind and in front of her. The cramped quarters of the train cabin meant the two elder Alicorns had to be on the chairs. Giving Twilight a completely unobstructed view of Luna’s teats.

She tried to ignore it, keeping her mind clear with mental exercises she was more than proficient in utilizing. All three of their minds had to be clear for the spell to work.

“You are not focused,” her mentor said behind her, causing her to jump.

“I’m sorry. It’s… it’s hard to concentrate with… certain things so close,” Twilight said and the gentle clop of hooves landing on wood in front of her drew her eyes to Luna. She was relaxed again, hooves on the bench. None of them were wearing regalia or metal of any sort as the metal would interfere with the spell.

“Perhaps we should remove distractions.” The suggestion was simple, worded more like a question than anything else. Twilight stared at Luna for a moment then looked back at her mentor. The eldest of the three alicorns present nodded.

“Would you like me to leave the cabin?” she asked teasingly. Luna answered first.

“Thou art just as much a distraction, dear sister.” Celestia would have spit out her drink had she been drinking anything. “Dost thou think I do not view her dreams as well as your own? Thine student fantasizes many a night about you. We should both appease her fantasies.”

The following two hours drew many a look from other train passengers walking by their cabin. No one bothered them. The train stopping at the Dragon Lands was their only indication that they needed to proceed. Celestia picked up the suitcase containing the monitoring equipment and the two Princesses departed the train. Celestia, for her part, had a rather rounded stomach. Luna was carrying the suitcase as she escorted her sister to meet their own escort. A dragon about twice Celestia’s size waited for them on the ground near the train station.

“Princesses. Dragon Lord Ember said you were coming for an experiment of a sort. Princess Twilight was supposed to be with you as well. Could she not make it?” he asked and Celestia just looked at her belly.

“She’s here. She is merely indisposed at the moment,” the elder princess said, shaking her hips slightly to make her belly sway. “I can release her if you’d like,” she said, and he looked at her for a moment. “I have all of her notes for the documentary.”

“If you have the notes, that should be enough. Let’s leave the area. I’m certain ponies wouldn’t take too kindly to what we are going to do,” he said, leading the two princesses from the platform. They followed him into the dragon lands, casting spells on themselves to increase their heat and lava resistance as they went. As they reached a more secluded place, the dragon stopped. “So… how shall we proceed?” the question was more directed at how they wanted the documentary to go. With Twilight Sparkle in her mentor’s womb, note taking would be slow.

“I shall be your temporary meal. My sister is quite adept at taking notes. I merely have to drink this to enhance my own resistances, and all shall be well,” Luna said, holding up a vial of pink liquid.

“Let me get this straight. You drink that… and I can eat you while your sister watches. Nothing will happen to the rest of my kind even after I add you to my ass,” the dragon said, and Luna stared at him.

“Not… exactly. The potion will keep us safe inside you. You won’t be able to digest me,”

“Are you completely sure about that Princess. Dragon stomachs are hardy places. We digest gemstones after all,” he said, sounding quite proud of something that was common knowledge.

“I am certain. Unless you are afraid.” Celestia looked at her sister and immediately knew what she was doing. Taking a couple of steps back, Celestia set up Twilight’s camera and quickly snapped the camera collar around Luna’s neck. The dragon looked at the smaller of the two ponies present out of one eye. “Perhaps you are afraid you cannot eat me. Perhaps you are afraid that I am too big a meal for you. Perhaps you are afraid that my sister will turn you to ashes should you try.”

Celestia looked at the dragon as he looked at her and raised her hooves. She would not intervene.

Luna continued her taunting. "Perhaps you are afraid it would mean war with Equestria. A war you could not win. Perhaps..." Luna was cut off as the large male’s head slammed into the ground where she stood, maw wide open. Celestia turned on both cameras and watched as the large dragon lifted his head, a chunk of dried molten rock tumbling from his lips. Tipping his head back, he gave a hearty swallow and Celestia watched on the monitor as the muscles in his throat worked Luna down the long chute. She wouldn’t narrate, not like Twilight or her friends would have. Celestia merely took detailed notes for Twilight to read later.

The small bulge that was Luna disappeared past the dragon’s collarbones and Celestia turned to the monitor to watch her sister’s progress. The throat was long, that much was certain, but when Luna entered the stomach, the vastness of it astounded them both. He was quite a bit larger than both of them. A glance at one of the screens showed Luna down the potion just off camera. The small vial that was thrown into the dragon’s magma like stomach acids was all the indication Celestia got that the potion was drunk.

Celestia, of course, was content to wait. Keeping her eyes on the screen to monitor her sisters progress, she wrote down a script for Twilight, trying to make it as professional as she could. She didn’t notice the movement behind her.

A roar was the only indication she got. Her horn lit and formed a bubble around herself. Not fast enough. The dragon’s maw clamped shut around her upper half, her forehooves simply dangling free as he lifted her up. A chomp. That’s all it would take. Immortal though she was, pain was still effective. Instead, he tipped his head back and swallowed. The camera on top of the monitors watched as she descended down his long throat to splash into his belly with her sister.

Unlike Luna, Celestia was unprotected by the potion, spells, or any other form of acid resistance. Luna was forced to watch as her sister’s coat and mane melted away in the powerful acids. She turned the camera away before just turning it off completely.

“So… we’re going to edit that out,” Twilight said, staring at the paused video. “Equestria doesn’t need to know that we can die.”

“Temporarily, Twilight. It didn’t hurt any worse than stubbing my hoof on the dresser,” Celestia said, her horn lit as her fur grew back. “It’s a shame about my mane and tail. Those will take some time to grow back. There is no spell for that. I am sorry I got you involved as well.”

“Still… for the sake of everypony, we’ll edit that out. Probably edit out the entire bit about you getting eaten. I can use Luna’s footage for the documentary.”

“You’re just jealous I got gobbled up by a big hunky dragon,” Celestia said, and Twilight blinked and looked at her mentor. She opened her mouth to protest only for the elder Princess to lift her up with her magic.

“You worry too much Twilight,” The younger princess didn’t even get a chance to argue as her teacher stuffed her into her maw and swallowed. A belch and contended sigh followed as Celestia rubbed her belly. “I’ll resurrect you later. It’s high time somepony taught you just how immortal Alicorns are.”

Author's Note

So... bit of digestion here. Kinda playing with "Alicorn Immortality" a bit. Just... seemed like it might fit here.