Instead, she realized with surprise, he’s squeezing himself through his trousers, running his palm along his solid length through the fabric. He’s keeping his expression still, but she can see the glassiness of his eyes, like he doesn’t even realize what he’s doing. The sight sends a jolt of warmth through her core, as Zabini switches to the other nipple, sucking and nibbling until her arms are shaking in the restraints.