[She nods and moves closer, waiting when she sees he'll be handling his own (erm) contribution to this, and moving her long sleeves away to expose her wrist too.]
Together then.
Ciel... It will be even more painful for a while right after this. I'm sorry it can't be helped. [He might know already but it's a fair warning. So with a long nail, she similarly cuts her wrist and positions it over Ciel along with Sebastian's wrist, so the blood mingles together before it drips down to his lips. The effect is near instantaneous.]