'Don't look, Dean,' Castiel said.
Dean looked into Castiel's blue eyes and saw pain and forgiveness there. Then he looked down at the angel's naked torso and saw the blood. Dean felt the knife in his hand. It was cold in his warm grip and wet with blood. Castiel's blood. Dean looked at unfamiliar blade. There were sigils along the tarnished metal, words in Enochian that he couldn't read. Dean swallowed hard, the realisation of what he had been doing, (of what they had made him do) firm in his mind. He was torturing an angel in Purgatory. He staggered back, images of his time in Hell flashing across his mind, the blood, the screaming. Suddenly he was back there and the images wouldn't stop.
He dropped the knife from his bloodstained hand and it clattered across stone.
That was something he had never done in Hell; stopped. A voice cut into the screams that Dean could still hear in his mind, a quiet but firm voice.
'It's ok, Dean.' Castiel said, his eyes pleading, 'I forgive you.'
'How?' Dean demanded, 'How is this ok, Cas?' He furiously started to wipe the blood from his hands, over his shirt, down his jeans, but it wouldn't come off.
'I told you once before, Dean,' Castiel said, I'm always happy to bleed for the Winchesters.' But there were tears running down the angel's face and Dean knew it was a brave lie.
Dean choked back his own pain and looked around him. In the darkness at the edge of a human/angel trap marked on the floor, the residents of Purgatory were watching.
'Pick up the knife, Dean,' Castiel said, 'It's ok, you can't hurt me.'
More lies. Dean stared, open mouthed, not knowing what to do.
'Pick up the knife, Dean,' Castiel repeated more firmly.
Dean looked around again and noticed that the creatures, so far as he could see of them, were becoming restless. He crouched down gingerly and picked up the knife. Then he approached the table and Castiel's strapped down vessel. Dean stopped with that on his mind; Castiel's vessel, Jimmy Novak. That was who he had been cutting into,
'No, Dean,' Castiel said, as though he had read his thoughts, which he probably had, 'It's just me in here. Jimmy died and went to Heaven a long time ago.'
'that doesn't make me feel any better,' Dean said through clenched teeth, 'Nothing could.'
'Just do it, Dean. So long as I know that you hate this, I can deal with it,' Castiel said.
Dean screwed his eyes up as tears formed. 'Cas,' he said, 'I can't.'
'Yes you can, Dean. You've already started,' Castiel said.
Dean didn't want to look, but he did anyway, saw the blood and the skin and looked away as soon as he could. He gripped the knife tighter.
'I'm sorry,' he said, 'I'm so sorry.' He couldn't bring himself to say Castiel's name as the knife went in.
The angel began to mouth 'I know,' but then he felt the knife and an agonised cry escaped his lips that made Dean close his eyes. Tears formed in his eyes, blurring his vision. His lips trembled, but his hand stayed steady.