A boy’s pretty sister uses him as a model for her human sexuality research paper

I was reading The Red Badge of Courage when my 16-year-
old sister came into my room without knocking, as
usual. When I wanted to jerk off I had to make sure she
was not home since the door didn’t lock.

“Hey dork,” she said gaily, and I saw she had her
little digital camera in one hand and a white, plastic
ruler in the other, “I need a favor.” I loved to watch
the way her parts jiggled and moved under her clothes.
My sister is a total fox.

I put down my book and smiled at her. She was very easy
to smile at. My sister was at least cute and probably
closer to beautiful. She has a very busy social life,
hooking up with lots of guys, and I suspected that she
was, as they say, sexually active, but until this day I
was not sure.

“This will only take a minute, honest,” she said,
grinning. “Stand up and drop your pants.”

“What?” I said rather loudly.

“Come on, Billy, I need some pictures for my
reproductive system report. It’s important, term paper,
you know, final grade.”

“Some pictures?” I said stupidly.

“I looked on the Internet, and I can’t find three or
four pictures of the same penis at different stages of
arousal.” She sighed theatrically.

“Pictures, you want to take pictures of my, my…”

“Yes, dummy. You do have one don’t you, most boys do so
I’ve been told.”

I just sat there shaking my head and feeling
embarrassed. Many times, more than I will admit here, I
have pictured my sister spread out and bare when I
masturbated, pouring out my spend on her big jugs,
spurting in her sucking mouth, only in my mind of

“So stand up, little boy. Here, take this ruler. Take
off your pants and hold the ruler beside your thing.”
She turned on her camera and stood waiting. When my
sister is waiting, it shows. Patience is not her main
virtue. She even tapped her foot.

“You are flat out crazy,” I said, looking at her
wearing her impatient face, one hand on her raised hip.

“Do you want me to show Mom your magazine collection?”
she asked nodding toward my closet where I had a hoard
of old Playboys and a few SI swimsuit issues, some of
them semen stained, all of them dog-eared, a lot of
them with naked girls that looked something like her.

“Please Dorrie, I can’t; honest I can’t,” I felt myself

“Sure you can. Nobody is going to know it’s yours. I’ll
just shoot ultra close ups. Please Billy. I’ll owe you
one. I have to get this finished by Friday, and I need
a good grade. Pretty please.” She batted her eyes at
me, and I gave up, trying not to see her nipples poking
at her thin shirt.

She looked so sad, so lovely, so sexy, so eager or
something. I stood up and peeled off my shorts and
boxers and took a deep breath as she went down on one
knee, adjusted my desk lamp so it illuminated my groin
and bit at her lower lip, squinting in concentration,
turning her head to the side. I put my hands on my
hips, holding my t-shirt high and made myself think of
nothing, looking at the doorway.

“Perfect,” she said, “it’s really small, all wrinkled
up, only about a inch, about the size of my thumb. Hold
the ruler on your thigh, right there.” She put it where
she wanted it, her hand grazing my balls. “No, that
won’t work. Your fingers cover the numbers.” She
grabbed my roll of Scotch tape and taped the ruler to
my thigh with the top end right up by my balls, poking
me in the crease, holding my scrotum on the back of her
hand while she adjusted the ruler, then got back on her
heels, aimed her tiny camera and fired three or four
shots. She looked up and smiled at me. “Now make it
bigger, a little bigger. It’s already poking out some
like a turtle’s head.” She prodded it with a fingernail
and I jumped.

“How?” I asked, feeling a mix of anger and
embarrassment. I mean a lot of guys had seen my prick
in the showers and stuff but no girl ever had and here
was this pretty girl smiling up at me even if she was
my sister, a foot away from it. I mean I was proud of
it and all, but I didn’t like the idea of showing it
off. I tensed my abs and shook my hips.

“Yeah,” she said, “like that. Good, good.” And she took
some more pictures.

I looked down and the stupid thing had swollen up a
couple of inches and hung down between my legs, kind of
twisted but definitely fatter. I could feel blood
pouring into it; at least that’s how it felt. It
quivered and the head moved side to side.

“Shake it,” my sister suggested. “I want it at rest,
aroused, tumescent and erect; at least four stages. How
big does yours get?”

“I never measured,” I lied to her as I reached down,
grasped my tool and shook it back and forth a few
times, slapping my thighs with its bullet head. It grew
so it was maybe four or five inches long and getting
fat too, but still just hanging there, limp, arched out
some over my balls. I took my hand away and she got
closer with her camera.

“Thanks,” she said, smiling and taking more pictures,
only a foot or so from my tingling cock. I tried not to
get excited, but I felt my heart beating harder and my
testicles throbbing. “It’s almost down to the five, and
I think it’s still growing.” She took two or three
more, moving slightly left and right. “Hold it still,”
she said and then she laughed and looked up at me while
my prick jumped. I held my hands behind me, resisting

“What’s tumescent mean?” I asked, trying to breathe
normally, tensing by groin, feeling my balls swelling.

“I don’t know exactly. It’s the term the books use. I
think it means full of blood, maybe excited.” She
reached out a hand and grasped my swollen rod, and I
squealed. “Don’t be such a baby,” she said, as she
stroked down and down and down, from the base to the
head, gently but firmly, raking with her fingernails.
“You’re getting there.” She backed away and took some
more pictures. “I may have to move the ruler ’cause
it’s getting fatter.”

I looked down and it was really long and growing hard,
jumping around but still hanging, looking like a piece
of pipe or garden hose. I’d swear it was halfway to my
knees and the veins on it were pulsing, the head
twitching, and it was kind of bulging out over my
scrotum which was also swelling, getting rounder.

“It’s almost six,” she said, “no, it is six. That’s
above average you know?” She looked up at me and
smiled, reaching out to touch the ridge of my cock head
and move her fingers around as if she were unscrewing
it. “Does it like that? Damn,” she said when it jumped
but did not rise. She flicked it with her forefinger
and I jumped and yelled something.

“I’m sorry,” I said, reaching down to stroke the dumb
thing and poke at my balls. It was hot and heavy, but I
certainly was not excited, not really. I held it in my
hand like I was weighing it and bounced it a few times.
I was really embarrassed as I stretched it out, using
both hands. Flabby was the word for it, like a big, wet

My sister put down her camera, went to my closet,
grabbed a couple of magazines and flopped out the
center spreads on the floor in front of me, a pair of
naked blondes with impossible breasts and no hips.
“Come on,” she said with a wide smile, “use your
imagination. I just need the last stage, the erection.
Wait a minute.”

She peeled the sticky tape off my leg and then attached
the ruler to my dangling cock with a couple of strips
of tape. “It’s almost six and a half, maybe seven,” she
said. “That’s terrific. I didn’t know you were so well
developed, I mean endowed. Now look at those sluts,
think about what you want to do to them.”

Nothing, absolutely nothing. My head refused to
cooperate. I could sometimes think it hard when I lay
on my back, but not this time. Talk about embarrassed.
I just couldn’t get it up.

“It’s shrinking,” she said loudly. “Don’t do that. Come
on, you quitter!”

She put down her camera, stood and stripped her faded
polo shirt over her head and tossed back her golden
hair. No bra; I had been right about that. I stared at
my sister’s bare breasts jiggling there right in front
of me, the nipples pink and upright, the jugs as big as
softballs, and I felt my penis hardening and rising, my
palms itching to grasp those beauties.

I put my hand down on my scotum and squeezed. It had
gotten hard and round, up tight at the base of my penis
which was still swelling and getting stiff and jumping
about like mad as it rose. I felt a bead of pearly pre-
cum oozing out and sucked in my belly while Dorrie took
pictures from several angles including two or three
with one of her boobs right on me as she shot down at
it, the camera at my belly button.

Then the tape snapped and peeled off and the ruler
dangled down. I pulled it free and held it under my
rearing cock which was sticking straight out in front
of me, looking like a tent pole or something.

“Eight plus,” my sister said. “Wonderful!” She handed
me the ruler. “Hold it there, right beside it. Almost
nine. Put it on the side, dummy. Its curved isn’t it?”
She adjusted the light and knelt again. “It’s
beautiful, Billy, just beautiful.” She reached out a
hand, pulled the ruler free and brought my long rod to
her lips, kissed it and licked it. Up it rose, pointed
at the ceiling, the way it gets when it’s fully
engorged, really excited, close to coming.

I whimpered as she picked up her camera and took
several more shots as my stiff member jumped up and
flexed, seeking friction, bubbling out goo.

“Thanks,” she said, picking up her shirt and bra and
hurrying away. “You were great.” She closed the door
leaving me with a painful erection and very blue balls.
I grabbed a couple of tissues and sobbed with relief
when I came, shuddering, sobbing as quietly as I could.
It was the most exhausting climax I had ever
experienced. I was emptied, maxed out, down on my

After supper she came to my room again, tossed me a
stapled paper and said, “Proofread it, dork. You’re
good at that.” She flopped on my bed and lay back on my
pillow. “Tell me what you think. I think it’s really
good. And I need an A. Mark where you find mistakes.”

It was about ten pages double-spaced so not much to
read but on every other page there was a 4×4 picture of
my penis with a caption under it. The lighting was good
and my pubic hair looked heavier than it really was. I
was surprised how the shape of my ball sack changed. I
had not been aware of that until the very end. It
really did get big in her pictures, like the size of a
baseball or something. But my cock was the star, and I
had to admit it looked good, strong and hot, and the
ruler helped too.

“It’s good,” I told her. “Clear and concise, no wasted
words, answers the question. I’d give you and A.”

“How’d you like the pictures?”

“You were right. They sure do help. You’ve actually
illustrated six stages haven’t you?”

“Um,” she said. “I was tempted to get a picture of you
ejaculating, but, well you know, that might have been
asking too much.” She sat up and smiled at me.

I laughed. “Now what are you going to do for me?” She
stretched out a hand and I gave her the paper. “”There
are a couple of typos, things the spell checker missed,
wrong words.”

She smiled at me. “If I get an A on this thing, two
people are going to lose their virginity at the same
time.” She hurried away, not bothering to close the
door. My cock jumped.