"You alone know whether it will harm your soul to help an old man avoid pain and humiliation," said Dumbledore gently "I ask this one, great favour of you, Severus, because death is coming for me as surely as the Chudley Cannons will finish bottom of this year’s league. I confess I should prefer a quick, painless exit to the protracted and messy affair it will be if, for instance, Greyback is involved – I hear Voldemort has recruited him? Or dear Bellatrix, who likes to play with her food before she eats it."