Jack lost his mind a moment when he sank his teeth into Ianto's shoulder and came insanely hard, so much so he almost passed out as he collapsed next to his lover. It took his brain a second to catch up with his mouth as his phermones eased off a little.
He swallowed hard at Ianto's question then remembered his promise to be honest with his lover from now on. "Uh yeah," he said breathlessly, "you know my constant need to flirt there is a chemical reason for it, it keeps my pheromones in check, if they get too high I go into heat and well you just discovered the result of that."