Jackson knew Klaus was possessive. He knew that could easily be turned on who he is possessive about as much as the person that he perceives as slighting him. But even with that, he'd never wanted anyone else to feed on him. It's a vulnerable thing and he trusts Klaus like he trusts no one else.

Jack had anticipated that Klaus would make his move at any moment but it still caught him off guard to be pressed against the wall. His hand went up to clutch at Klaus' shoulder, a shiver of anticipation as the other's breath teased at his skin a pleasurable tingle. Then the fangs breaking his skin, Klaus drinking from him and his head falls back. He leaves himself open to Klaus, the pain borders with pleasure. Klaus isn't vicious with this and well... for some reason, Jack had always liked it.

The sounds that came from his mouth, breathy and sharp were more moan like than a cry of pain.