How about anal?

"What if I thought about doing stuff like... anal stimulation?" Nate asked.

"That is perfectly natural," she reassured him."It is perfectly natural for a young man of your age to explore areas like that, albeit safely of course. Uh, If you would bend over we can see what is going on 'down under'." He did as she requested and leaned over the table, sticking his rear end out a bit.

"Well first of all, anything going in the anus rather than out of it will require proper lubrication. It should not include any sort of **** such as soap or hand...." She kept talking but Nate began drowning out her voice unintentionally as he began focusing on the feeling of the gloved finger entering his asshole. It felt weird, but not unpleasant. He began to shift slightly in place to compensate for the new sensation. Meanwhile, Mrs. Joy was still stuttering about how to safely participate in anal stimulation/sex. Did he even enforce at least an element of susceptibility to her personality, or was she just this naive? Speaking of which...

"Did you know that spankings are actually good for anal?" Mrs. Joy said without thinking. The moment she realized she heard herself say it she blushed and laughed to herself. This caused her finger to move farther inside Nate, all the way down to the knuckle.

"Are you serious?" Nate asked, feeling new sensations.

"Well... yes, actually," she replied, blushing. "It causes blood to flow to the affecting area, helping you relax and reflexively clench up, possibly causing damage."

"Science is amazing!” Nate said without the slightest sense of irony. He meant it.

Mrs. Joy laughed when he said this. She appreciated that he could have a sense of humor about this. It immediately diffused the tension so palpable she could feel it in the air, mingling with her sweat in reaction. This put her at ease and the tension just melted away and she couldn't help from smiling.