Surprise her with your cock.

You take your hands off her ass and prepare to move on to the part you've been waiting for, when an idea occurs to you. Kat still doesn't know the extent of the inspection, which gives you an opportunity to surprise her with it.

"Why don't you go bend over the side of the couch?" you suggest.

She shoots you a briefly skeptical look over her shoulder before standing next to the couch. "Um... sure," she replies, bending over the arm and leaning on the cushions. "I suppose you're going be... feeling my crotch next?" she asks hesitantly.

"Yep. You're doing great so far," you reassure her, though you don't imagine her performance is the source of her hesitation. "This will give me the best access to it."

"I... guess that makes sense," she concedes.

You crouch behind her and admire her pussy one more time. It's separating some from the position she's in and from her involuntary arousal, and you think you can just peek into the depths of her vagina. Reaching out to finally touch it, you weave your fingers into her folds, between and beside her labia. It's so soft to the touch and just a little moist with her secretions. Sliding your hand out, you place your at the base and trace the perimeter of her outer labia. Noticing her clit at the far end, you place your finger on it and make just a couple small circles with gentle pressure.

"Oh!" she exclaims softly. "Is this part of the inspection, too, then? Not that it doesn't feel nice, but... uh..." she trails off, marginally uncomfortable.

The nice thing about sweatpants is that there's no buckle or zipper to make noise. Confirming that she's looking away from you, you stand up and quickly pull the elastic waistband down, making sure to extend it clear of your erection. Focusing on your prize, you place a hand firmly on each of Kat's hips. In her peripheral vision, you see her lift her head quizzically, but before she can turn around to investigate, you've placed the head of your cock against the labia you were caressing a moment ago, and without hesitation you thrust into her, practically pulling yourself inside. You briefly feel the contours of Kat's vagina sliding over your shaft before you come to rest, those same warm contours blissfully squeezing you.

Kat's reaction is immediate, more reflex than thought. Her arms straighten in a vain attempt to stand, but with your body anchoring her to the couch she can barely lift herself above horizontal. "What the fuck?!" she exclaims, and even as she does you're already pulling halfway out in preparation for a second thrust. This one is just a little slower as you allow yourself to actually feel the friction between your genitals. Pausing briefly with your cock firmly inside Kat, your thighs resting against hers, you consider whether to pause your animal victory and offer her an explanation.