"Jeff? How did you... How are you so small? And why were you in my undies?" Diana asked, somewhat unsure about mentioning her diaper.
Jeff, unaware of what to say, stutters out "I-I don't know! I was sitting on m-my bed, and then suddenly appeared in there!", silently praising himself for his last-minute lie. It was partially true though.
"Hmm... I don't believe you. But I'll play along for now..." Diana had started thinking of what she could do with Jeff in this state. Jeff was clearly worried; He knew his sister was too innocent to do anything bad to him, but at the same time this situation was unique.
"Well, you'll need protection if you're this size! So... hmm... Where should you be kept... Oh, I know! About the safest place you could be is in my mouth! Nothing can happen to you in there, Teehee!" So, as Diana finished talking, she lowered Jeff to her mouth, and shoved him in there. Immediately she felt the feeling as a little weird, having her naked brother in her mouth.
Jeff quickly voices his concern; "What if you accidentally swallow me! I don't know what could happen from there!", to which Diana responds "I won't eat you! It's funny how you could even think that! Though, speaking of eating... I can go for a snack!"
Off she went to get a snack. On the way down, she had forgotten Jeff was in her mouth; Out of the cabinet, she grabs out some oreos, which she then starts munching on. Jeff had an up-close look of his sister eating, and felt like he was going to puke, as half-chewed food often causes.
As Diana finished the first oreo, she swallowed, which accidentally caused Jeff to get swallowed as well. Jeff, now falling down her throat, had panicked and immediately started grabbing at whatever he could to stop the fall...