Melanie walks down the hall towards her first class of the day. It's her second semester of college, and she couldn't be happier. She's finally getting the chance to become a veternarian, a job she's always deeply desired.
In her time at college, she's made friends with nearly everyone she's spent much time around, being so sweet and charming that just about everyone loves her. Even those she isn't good friends with she's at least acquainted with on good terms.
One such acquaintance is Arnie, a heavy-set brown horse who is studying to become an engineer. They get along quite well, but they haven't been around each other enough to really become friends, not sharing many classes. Still, she's always happy to see him around.
Arnie happens to have a class on the opposite side of the building from Melanie, and as such, he turns the corner into the same hall, walking in the opposite direction. Just as he turns the corner, he bumps into Melanie, who gets thrown off-balance. Melanie jerks forward to try to avoid falling backward right as Arnie trips as the impact makes him stumble.
As a result, Arnie ends up sitting on his ass on the ground, Melanie's head and shoulders in his maw and the rest of her leaned over his fat gut. Arnie's eyes dart around, stunned by the sudden turn of events and not quite processing yet what's happened.
GRRWWWWLLRGLLLLLLE
Arnie's stomach growls loudly; he hasn't had time to eat breakfast, waking up quite late. Without thinking, he starts to swallow Melanie down rather quickly. By all means, he wouldn't normally eat anyone, certainly not someone he's well acquainted with. However, in the sudden unusual circumstance, his brain short circuits a bit, and he takes the opportunity to solve the problems of Melanie in his mouth and his own hunger at the same time.
Melanie kicks her legs and thrashes as the hungry horse stuffs her deeper into his maw, reaching her hips then shoving in her legs. He swallows loudly, and Melanie disappears. Arnie lets out a loud belch.
GULP UUUUUUUUUUUUUURRRRP
The horse sits up fully, and it starts to dawn on him what he's done. He first looks around to see if anyone saw him. There are no cameras in the hall, and with it being so early, nobody else is around. 
He then looks down at his Melanie-stuffed gut. She's hardly visible beneath his thick layers of fat; it'd take a close inspection to realize anyone is trapped inside. Her squirms, though he can certainly feel them, are too weak to move much of the fat between her and the outside world. Any sound she makes is similarly muffled. Unless someone put their ear up against his gut, they'd never know.
RRRRRGGLLLL GLLRG
Arnie gets up and continues on his way to class. He could never explain this if anyone found out, and he was hungry anyway. He tries to just not think about it and carry on with his day as normal, despite the arctic fox currently melting in his gut.
Sitting through his classes with his gut so full is terribly awkward, and the gurgling of his gut gets him a couple of odd looks from his peers. Fortunately, it isn't unusual for his stomach to be so noisy, even without Melanie churning in it. As such, he makes it through the day without a hitch.
PPFFFRRFFFLBLLRFFFFF BLLRGBHFFLRBLLLT PLOP PLAT FFBLRGGHHH SPLAP
Arnie grunts as he forces Melanie's remains out his backside into one of the campus's public toilets. He's on his fifth flush, and more of his former acquaintence is still coming out. He feels a femur slide out with another massive log of shit. Her skull follows.
Finally empty, he huffs from the effort and leans back on the toilet to take a breather. After a moment of rest, he stands again and pulls out a couple of plastic bags meant for picking up dog turds and maneuvers the large, unflushable bones into them, being careful not to touch them with his bare hands for how filthy they are. He stuffs the bagged bones into his backpack. He'll have to bury them later.
"Well, uh, sorry, Melanie, eheh. You tasted good at least..."
FFLLLLLLLLLLLSHHHSHHHHHHSHHH
Melanie was a popular student at the college, and rumors naturally popped up regarding her disappearance. Some say she was involved in organized crime and fled the country. Some say she was murdered by a serial killer. Most believe she just moved out. Really, though, all these theories are horse shit.