Derek glances up from where he's very thoroughly licking the back of Stiles' knee, one hand braced against the boy's thigh to hold his leg at the angle he wants it. "Mm?" he smirks, arching an eyebrow before returning to his work sucking a decent sized hickey into Stiles' lower thigh.

It's fantastic. He's only just started, and already Stiles is getting impatient, and Derek can't help but be amused.