Well, it wasnt in the context of an exam, but I remember my first bdsm girlfriend from back in the day.
She had one of those old iron-frame beds, where the mattress sits on top of a metal mesh-like spring. Tradition box springs are not required for this type of bed.
I dumped the mattress off the bed, stripped her nude, and laced her to the iron mesh. Her arms were laced close at her side, and her legs were laced open in a V-shape (obviously. lol). This was not an unusually tight lacing, but I did not allow much distance between loops, and I used a LOT of rope. She could undulate slightly against the spring, but thats all.
I then spent the next hour edging her with slow-strokes. She quivered like a new-born pup, and occasionally spasmed just short of a climax. When her mind "went someplace else" and she started softly babbling nonsense sentences, I brought her to completion, and gently ended the session.
It wasnt a particularly perverted session per se, but it was super-hot to see her mind transition on the edge. Thereafter, I had hoped to get her to lose control of her bladder, and involuntarily discharge urine to a bucket beneath the bedspring, but sadly I was never able to achieve this.