Chapter 3

Becki, our fifteen-year-old blonde bi-sexual woke up spread-eagled, face-down naked on her bed. She gingerly rubbed her clit and sleepily pushed a finger into her cunt and was delighted that the numbness from yesterday had worn off. Becki was humping a pillow when big sister Faye walked in and kissed all down her pretty tanned back and licked into her pale sore bottom.

“Yuck, this tastes of suntan oil and spunk, what have you been up to?”

Becki abandoned the pillow and cuddled Faye as she had since before puberty, wrapping her legs around Faye’s and humping her hip bone, whilst giving a full account of the mk2 masturbator she Molly and Gemma had enjoyed on the train and at the seaside. After Becki described the delicious sensations the mk2 made simultaneously in her nipples and clit, she swung her legs around to be fully interlocked with Faye.

Faye slipped a short squishy double-ender between their moist pussy lips and pulled hard on Becki’s hands to engage it fully into their cunts. Later they showered together, climaxing again as they swapped Mike’s showerhead dildo with the pulsating water spray into their clits and g-spots.

Back in Mike’s workshop he had uploaded all the monitoring data from the 3 thigh strap computers and was building up on-screen a three-dimensional internal picture of Gemma’s cunt from the temperature and moisture readings. He could clearly observe each time she had climaxed and which programmed stimulations caused it. Mike had stored the discarded three mk2 devices in a plastic bag after the girls had left.

The next morning Pam easily identified which had been worn by each girl from the taste of the remaining pussy juice. Pam loved the internal heat image of Molly’s cunt and arse and superimposed it onto close-up photos of her dark pubes and bum to create a panoramic series of composite internal/external views. Timmy had never realised from school human biology lessons how thin the wall was between Molly’s two openings and how easily deep anal penetration caused her to climax.

Timmy had managed to hold focus on the mk2 in the cart-wheeling video flashing into view each time Gemma’s cunt was above her head. Mike realised the technical need for an internal accelerometer in mk3 to determine which way up the girl is, and measure her contractions directly.

Mike received an order from Molly’s games mistress and several of her friends after watching the videos and trying the nipple-ring stimulator in its proper place and attached to their labia. Pam and Mike researched the web for dildo designs, and Pam loved the ‘strapless strap-on’ Feeldoe. This was advertised as having a bulbous passive end that fits snugly into her cunt and the active end for probing her partner, leaving both hands free. Mike ordered a genuine model and several cheaper copies for Pam to try out with her adult friends and the girls at the next Sybian Club meeting.

Faye and Becki came over to Mike’s and he carefully watched Pam getting sandwiched by the two sisters wearing bikini tops and Feeldoes, penetrating her back and front simultaneously. After a few changes of position and dildo model, they all agreed that the version with an additional bum-hole bulb provided the best fit, which stayed in place even with vigorous fucking and pussy juice oozing down their legs.

This experiment and the internal 3-dimensional data led to the design of mk3 to automatically adjust to any female pubic shape or size, instead of being custom designed for each C-to-A distance. He re-introduced a lightweight hip belt supporting the almost-rigid thigh straps where the self-guided flexible pussy and bum probes connect. The device was completely open front and back to allow plenty of cooling airflow, with all batteries, comms and control devices on the hip belt.

Molly, my step-sister, drooled in delight when she pulled on the mk3 prototype a week later, and I filmed her convulsing through its first probing and her rapid climaxes. Once the middle and rear probes had moulded themselves to their owner’s internal dimensions the front probe was free to roam around and massage her clit, or under command to search out other cunts, turning into a ‘strap-on’ penis.

Pam found that the front probe rotated so she could fuck Faye either face-to-face, from behind, face-to-feet or in her favourite position - fully interlocked. Any hip-thrusting action was automatically magnified into the ‘penis’, for pounding the games mistress or could be reduced for fucking very young girls. Bluetooth was much enhanced, automatically sending the up-skirt videos to anyone in a 20 metre radius, and allowing control from any PC or iPhone; he added WiFi for the Nintendo DSi console.