It's a strange thing, feeling what Sirius is while he's the one providing it. The lack of sensation, taste, and everything else makes him very singular in what he's doing. All he can tell is that when he's doing well, the peals of lust almost make him falter, so he reaches up to grab hold of Sirius by the hips and hold him in place to get a little better leverage.

And the minute he feels that hard grip on himself, it's another dizzy spell waiting to happen.