[It's ironic that on one of the occasions when he actually set out to try and talk to Spike without aiming for anything like this is when it happens, but perhaps that's just their relationship all over.
And really, it's quite a relief not to have to work at understanding everything Spike's saying any more. Jack may not be a poet, but he is intimately familiar with the language of kissing, and he gets a good deal of why the fangs are out, that it's not just about exciting him (which is definitely working) and is also about making this different from being with Ianto.
And he is completely fine with that. It makes it completely different from him being with Ianto too, and that, for him, is what polyamory is all about. He meets the kiss with equal fervour, his hands coming up to to Spike's shoulders and head, pulling him in just as enthusiastically as he's being pulled in. Pushing in, moaning and panting, crying out as his lip tears against a fang and blood starts to seep out into his mouth.]