Disclaimer: I don't own SPN.
So, uh…yeah.
"I believe I have a cure for the Mark of Cain," Castiel said solemnly. Sam immediately snapped to attention.
"Well?" he demanded.
"An advertisement played on the television," Castiel began. "And I couldn't help but notice that the product they were advertising was very effective in curing the man of his condition."
"Spit it out!" Sam said. Castiel frowned at him.
"How can I spit it out?" he said. "I have not ingested it or put it in my mouth…"
Sam just shook his head.
"Tell me what it is," he said. Castiel reached into his pocket and pulled out a small packet, which he gave to Sam. Sam spluttered and choked with laughter.
"Cas, this doesn't actually work!" he said. "It's just a commercial! They use two different actors!"
"I don't understand," Castiel frowned. "I thought the point of advertisements was to inform people of what their products do."
Sam was still shaking with laughter.
"The point of ads is to get people to buy the things!" he said. "I mean, sure they have to tell you if their things do anything bad and any side effects. But the point of ads is to make people interested in buying their products."
"So this won't work?" Castiel looked at the object in Sam's hand forlornly. "I went to a great effort to obtain that and it doesn't even work?"
"It can't hurt to try," Sam snickered.
-oOoOo-
"This is for your own good!" Sam yelled as Castiel restrained a furiously struggling Dean.
"It'll never work!" Dean bellowed, struggling and twisting in Castiel's grip. "Let me go, dammit!"
Sam ripped open the packet and tried to force the object into Dean's mouth but Dean howled and kicked Sam's arm away.
"Dammit! Just eat the frigging Snickers, Dean!" Sam exploded.
"I don't wanna!" Dean wailed like a petulant child. "Let me go! I wanna go kill stuff!"
"This is more serious than we thought," Castiel said gravely. "I apologise, Dean, but you leave us with no choice."
He pinched Dean's nose. Dean stubbornly held his breath but eventually, the instinctive desire for oxygen won out and he opened his mouth to gasp in air. The minute he did, Sam shoved the chocolate bar into his mouth and covered it so that Dean wouldn't spit it out. Castiel released his nose to allow Dean to breathe. Dean reluctantly swallowed the chocolate bar and then they waited in silence.
"Told you it wouldn't work," Sam snarked. But he spoke too soon. The Mark of Cain on Dean's arm began to glow a bright red and Dean threw back his head and howled as light streamed out of the Mark, while the Mark itself began to disintegrate. Sam thought he was going crazy when he caught a faint whiff of nutty chocolate.
"I can't believe that actually worked," Sam said in shock.
"I told you," Castiel said smugly. "You're not you when you're hungry." He bent down and helped Dean up. "Better?"
Dean nodded shakily, staring at his Mark-free forearm.
"Better," he replied.