“Let me see what’s next on the list,” said Beth as she consulted the study instructions. “Oh, my, you should really like these next few tests, Jim!”

“Why, what are you going to do now?”

“Next up is 30 seconds of light testicular massage.”

“You mean, you’re going to rub my balls?”

“Yes, Jim, that’s what the instructions call for.”

Without any hesitation, she placed the fingers from both of her hands on my testicles. I felt some of her fingers underneath, cupping and holding them, while the fingers of her other hand rested on top. Once her gloved fingers were in place around my balls, she began to massage them, slowly at first, then with ever increasing speed. Since the skin was already pulled tight by the strap, they seemed especially sensitive to even the slightest touch from her fingers. I looked up to see that the laptop screen had a timer running that was counting down the seconds, 23, 22, 21. Her fingers felt wonderful as they caressed my balls, and I felt myself becoming more aroused with each passing second.

“Time,” called out Ashley. Beth immediately stopped rubbing me and removed her hands. Part of me wanted her to continue, since it felt so good. But deep down, I was glad that she stopped, since I knew that her continued attention to my balls would only cause me to ejaculate, and I didn’t want to do that. I also didn’t know what else the girls had in store for me. I didn’t want to get too excited right away.

I looked over to see that Ashley and Beth were once again looking at the readings on the laptop screen. While Ashley continued to record my current measurements, Beth retrieved a tube of lubricant from the shelf under the laptop and proceeded to squeeze a generous supply onto the index and middle fingers of her gloved hand. As soon as I saw that, I had a pretty good idea where those fingers were going.

“I know you’ll like this, Jim. It’s time for a little light prostate massage,” Beth said. “This will feel just like the prostate exam that Ashley did earlier, but I’ll be doing it continuously for 30 seconds.”

Without any other warning, I felt the coldness of Beth’s lubricated finger on the entrance to my rectum. Just as Ashley did earlier, she applied firm pressure until my anus accepted its new invader. Now her first finger slipped into me, followed immediately by the second finger. Her fingers found their way to my prostate and she began to press on it. My body involuntarily jerked as she first made contact. She then began a cycle of pushing on my prostate for a second or so, and then releasing for an equal amount of time. She repeated this cycle of pressing and releasing over and over again. As she continued to rhythmically stimulate my prostate, I felt the urge to ejaculate begin to build up. I looked at the timer on the laptop – I still had 23 seconds to go! I didn’t know if I would be able to hold out that long.

“You look like you’re really enjoying this, Jim,” Beth said to me in a somewhat hushed and calming voice. “I know how much you like to have someone’s fingers up your ass like this. I know that Mandy sometimes does this to you, she’s told me about it.”

I didn’t know why Beth was bringing this up right now, but I didn’t answer her. I was just trying to concentrate on getting through this part of the test. I looked at the laptop again, still 15 seconds to go.

“And Jim,” she continued, “do you remember that time last summer when you and Mandy were fooling around on the living room sofa? When you didn’t think anyone else was at home? Well, I was home! You didn’t see or hear me as I came downstairs. I quietly watched as she had you get on your hands and knees on the sofa, and then she stuck her fingers in you, just like I’m doing right now.”

As the seconds finally ticked down, Beth removed her fingers from my ass and discarded her exam glove.

“Even though you were with my little sister,” Beth continued, “I still thought it was hot as hell to watch.”

“Beth, we had no idea you were there,” I said, breathlessly trying to regain my composure. “You should have said something.”

“What, and ruin the show? You don’t have to apologize to me. Like I said, I enjoyed watching you.”

“I’ve got his measurements all recorded. Are you ready for the next test?” asked Ashley. She was talking to Beth, but I noticed that she was looking down between my parted legs as she spoke.

“Sure, let me take another quick look at the list to see what’s next.” Beth picked up my folder of paperwork and scanned the study instructions one more time before pulling on a fresh exam glove. She then retrieved the next item to be used on me from the shelf below the laptop. As she held it up for me to see, my general feeling of embarrassment quickly turned to fear and dread.

“I’m sure you can figure out where this goes, Jim,” she said to me with a smile. She held up a dildo that was made of a hard black rubberized material. It looked like it was about 8 inches long and maybe 1 ½ to 2 inches in diameter. It wasn’t anatomical looking, meaning it didn’t look like a real human penis. It appeared to be a fairly plain cylinder.

“No, I don’t think so, I don’t want that thing in me,” I protested. I tried to move my hands but they were still securely fastened to the exam table. Likewise, my legs were secure in the leg supports. I was helpless and had no choice but to endure everything that the girls were about to inflict on me.

“Don’t worry, Jim, it will be fine,” Beth said to me. I looked up to see that Ashley was now covering her mouth with her hand to hide the fact that she had been laughing. Beth now took out a condom and unrolled it over the dildo.

“This will make the cleanup a little easier,” she said. She now retrieved the tube of lubricant and applied a generous portion over the entire length of the sex toy, spreading it with her fingers until the entire surface was covered. “We’re going to do two different tests with this, Jim. First, I’m going to insert it all the way, and then we’ll record your size for 30 seconds without any movement at all. Then after that, I’ll manipulate the toy in and out to further stimulate you for another 45 seconds. Understand?”

By the time I silently nodded, Beth had already begun pressing the lubricated dildo against my anal sphincter. As soon as I opened up to her, she began to apply firm and constant pressure to insert the toy into me. As it slowly slid into me, I first felt myself being stretched to accommodate the girth of the toy. Then as she slid it in deeper, I felt it completely filling my rectum. Once she finally had it all the way in, she signaled to Ashley to start the count down. As I watched the timer on the laptop count down the seconds, I felt the fullness of the toy inside of me. I looked down between my parted legs to see that my cock was now fully engorged with blood and appeared to be rock hard. The strap that was still in place behind my balls was slowing the release of blood, causing me to be pumped up more than ever. I couldn’t see them, but I could feel that my balls were still pulled forward and away from my body due to the tightness of the strap.

“Time,” I heard Ashley say.

“Alright, now for a little movement,” said Beth. Ashley reset the timer to 45 seconds as Beth slowly withdraw the dildo from my rectum. She withdrew it until it was almost all the way out, and then reversed direction and inserted it all the way back into me. She then began to repeat the same movement, withdrawing it and then inserting it again. Each time she repeated the cycle, she quickened the pace, going faster and using more force. After just a few seconds, she was pumping the dildo in and out of me in an almost continuous motion. Each time she thrust the toy into me, my body involuntarily jerked and my breathing quickened and became shallower. For some reason, Beth now decided that this was a good time to continue the conversation that she started earlier.

“And Jim, that night with you and Mandy on the sofa -- I watched the entire thing, every bit of it. After she got you warmed up, you returned the favor by using your tongue on her. And when both of you were hot enough, I watched her straddle that cock of yours and then you guys went at it like rabbits. It was amazing to watch. At that moment I wished it was me on that sofa instead of Mandy. I got so hot watching you that I had to go back upstairs and take care of my own urges!” Beth looked straight into my eyes with a wide grin as she was talking.

“I didn’t know, Beth,” was all I managed to say.

“I never dreamed that I’d be here right now, doing this to you,” Beth said with a smile.

“Time,” we heard Ashley say.

Beth immediately withdrew the dildo from me and peeled off the condom.