When Peter felt her tail curl against him, he found the feeling to be different, somewhat surprising, but also welcomed. As he became warmed and more comfortable with his lips against hers, the hand on his back only grew more confident, gripping a bit tighter and pulling her closer to him, while he, himself, leaned forward to put more assertion behind the kiss.
He had to admit, he hadn't really understood where they stood before this evening, and didn't think anything like this would happen; yet, now that it was he couldn't have asked for a better outcome. He liked her, and while it perhaps didn't cement them in any form of relationship, it did mean that their crushes were mutual and made him feel like he could finally stop questioning things around each of them, and be comfortable.
The free hand dropped down to her leg, which he allowed his fingers to softly squeeze while the underside of her arm brushed against her bushy tail. Finding the warmth and softness rather enticing, and he grew suddenly much more comfortable with the tail than he thought he would have.