Trapped

"And will you, Professor Jonathan Chase, take this woman..." "Fuck yeah!"
"Aw c'mon, John, now let the good priest finish his yadda yadda!" Ty chimed in. "And it's 'Yes, I will', although a 'Fuck yeah!' probably also legally counts as a consent."
"...then I hereby declare you husband and wife. You now may..." continued the priest, somewhat rattled.
"Mmmmpf!" Brooke reacted a bit faster and smooched Jonathan to the church floor. "You are trapped forever now, Professor!" she exclaimed when their lips parted for a moment to get some air.
"Dear couple!" the indignated priest interrupted. "I understand the passion of young love, but could you refrain of doing it like animals in my church?"
Naturally, this statement also laid Ty flat into the aisle. "What's so funny about..." "Sorry kahuna, mwhahaha, we're all a bit over the top today, snicker, I carry off the two love turtles in my van before something hahahaha indecent will happen."

Later at their new home...
"So what will you turn into? Detective, any chance you might be able to take an elephant? Although that's still smaller than my ni..."
"Get out already, Ty." Professor Chase cut him short. "And I don't want to hear the N word, not even from somebody with the license and evidently with a glass of altar wine too many." He dialed a taxi for his friend. "If we ever talk of size, then about the size of our future family. And the size of the apartment where we spend our wedding trip." "And the size of my gun in case you don't immediately vanish into the cab that just arrived! Like if I'm into bestiality!" Brooke giggled. Pegged by Brooke on one and John on the other side, Ty staggered to the waiting cab and exclaimed "Chase, you're such a lucky bugger!" before he was carried off horizontally. "That's that. And NOW we do it like animals!" Brooke goatishly stared at her new spouse.

Brooke sprawled stork-naked on the bed and spread wide. "Like what you see? But be careful, as soon as it captures you, it never let's you go again!"
"If I turn into a dog, maybe," the Professor murmured to himself. "What?" "Nothing. Maybe later." "Now let me get off this silly tie! Damn, you even keep it somewhere in your animal forms! And away with your trousers! AAAAAH! My God! It's a trouser snake! It will spit its venom at me!" she feigned
Chase laughed. "I wonder if I can ever cure your silly fear of snakes. They are so maligned. In fact, they have ssssome interessssting traitsssss..." "John, you won't..." "...like forked tonguessss and inflatable hemipenesssss..." "No! Stop it!" "...there issss no need to be afraid, it'sssss not that I will eat you alive...OK, I WILL eat you alive...but I ssssuppossse you like it..." "JOHN!!!" "Ssssss."
And John had turned into a giant anaconda who took Brooke into a firm hug.
"NOOOO! NOOOO!" screamed Brooke.
And then the snake demonstrated what a forked tongue was good for, apart from gauging small temperature differences.
Protip: You should consider getting a forked tongue yourself and practice some cunnilingus on your girlfriend. In less than a minute, her brain will have turned to jelly and she will be your love slave forever. Void where prohibited.
"YESSS! YEEEEEES!" screamed Brooke, her vagina walls beginning to pulsate.
Snake-John judged that he could have some fun now either. The coils contracted, tying Brooke up and bringing her mouth and her pussy close together. Surely this position was a bit too unconfortable to be listed in the Kamasutra, but she was way past protests. And then huge hemipenises slid up her orifices, one into the mouth to muffle her screams, and one into the vagina to drive her completely insane. Since they were inflatable (didn't you pay attention or what?) they fitted perfectly.
Brooke turned into a mass of orgasming, writhing flesh. Her vagina contracted firmly around the snake, who now came too. The "venom" gushed into her womb and her throat. She gulped for her life, then her body went limp, unconscious, satisfied and impregnated.

After Brooke had regained consciousness, she was Johns love slave forever. (Told you, didn't I?) "OK, NOW I'm into bestiality" she sighed exasperatedly. And then they tried out a few other animals.
She took a rhino by the horn. ("Better than grounded and sent to Asia, right?" [...] "YEEES! YEEES!").
She took a lion. ("Not recommended. Lie still or the barbs on the penis will impale you for good." [...] "YEEES! YEEES!").
She took a dog by the knot. ("It will lock itself right at the entrance of your vagina, where it pleasures you most...and you can't escape." [...] "YEEEES! YEEEES!").
She took a dolphin in the bath tub. ("Such a dork can do most interesting things inside you." [...] "YEEES! YEEES!").
She took a horse by the flare. ("It will lock itself inside your womb, and you will be stretched beyond recognition...are you sure you can take it?" [...] "YEEEEEEES! YEEEEEEES!").
When she tried to blow-job an elephant, even if John was so considerate ejaculating quite before her mouth and not deep in her throat, he still nearly drowned her in cum. They decided to call it a day.

9 months and 1001 orgasms later...
John and Brooke lied naked on the bed again. "Oh God, look how plump I am. I think sex is out of question." "And if I turn into a snake again and lick you senseless?" "I love forked tongues but I STILL LOATH SNAKES! Hmmm, when will they come out?" "Giving that you expect twins, your labour is overdue. You're sure we shall not drive into the hospital and do a cesarean?" "If you have knocked me up with an elephant and I'm in for another year, I so kill you, John!" "Eh, no, the ultrasonic was perfectly clear..." "Wait...something is writhing inside me..."
And then everything went very fast.
Two tiny snakes slid out of Brookes vagina and headed straight for her swollen breasts, milking her for all what it's worth. "Right. I forgot. It's hereditary." "Oh look, John, how cute they are! I LOVE SNAKES I LOVE SNAKES I LOVE SNAKES!"
Mothership. It turns your brain into jelly either.
And since Brooke was still properly stretched, they tried out if she could take an elephant ("YEEEEEEEEES! YEEEEEEEEEES!"). But after that, her twins turned back to normal form and they took their whole attention, and baby care is annoying and a drag, even if or especially if they can turn to animals, and in any case no theme for a porn story and we call it

The End