Percy wasn't stupid. He knew exactly what Cass was doing, but as long as he didn't overdo it, then he would be more than happy to enjoy what was happening. That didn't stop him from keeping a close eye on Cass, making sure his breathing was regular, and there were no sign of pain in any way.
He closed his eyes despite himself, appreciating every touch, every tingling sensation that Cass was evoking. He loved this, loved the way Cass could make him feel, the way his body responded. "Oh God, I missed this."