Can he do it? He might actually be able to do it, revelling in the heat and motion, filling his nose with the scent of Jack and future pheromones and oh okay yeah as long as they keep this up for a little longer he'll be able to reach his goal.
His fingers fist tighter in Jack's hair, pulling his head to the side so Spike can sink blunt teeth in against his skin in a hard bite — hard enough to bruise, not hard enough to draw blood. No fangs, no ridges, just the two of them grinding against each other and him remembering how easily Jack fell apart that one time in the park, in the dark, long before he even entertained the idea of actually getting into the pants of Captain Woodstock.