Not on the seats! On the engine, I think. Or the hood? Well, anyway.

[She waves a dismissive hand, presumably at the very notion of getting blood all over the nice interior of the car.]

It sounded like making a golem, except instead of a golem, it's the car. And, well, instead of animating it with rituals like a golem, you...summon a demon into the the blood you marked it with and somehow it possesses the car. But in theory it was very interesting! And terrible.