Black magic is not free. You have to pay.
"It's aroma." Yusuf jiggles the cardboard lid off. Inside is something the texture and colour of rich compost but with a sweet and sickly and pungent fragrance. "It's for corpses. When they decompose they start to smell. You can use this."
"They're mostly used for bad purposes," he adds. "If you want something good, you simply pray."