The thing is, by now Steven is actually used to people being fine with being strangled. Well, by people he mostly means Jack, who has a bit of a fetish for it, both giving and receiving.

It would be accurate to say that erotic asphyxiation had been a key component of their sex life this last month.

So when Lydia takes this so easily, closing her eyes, it reminds him of strangling Jack and Steven finds himself adjusting his hands subtly, to the position they would be in for sexy times with his boyfriend. And when she's seconds away from passing out—

Well. He lets go, pretty much on instinct.

Oops.