Severus thrashed around, but not because he wanted to get away. No. Sirius's weight was perfect. His body arching against his own was even more perfect. The Slytherin yowled. He arched up against Sirius's naked belly. When his lips came into range, he bit and nipped and licked at them.

Passionate? Yes, Severus burned so hot under such a cold exterior that it was like being with a different person. Severus thought that way too. With Sirius...he could be someone else. For just a little while.