Brood Mana Absorption

Sorin spoke quickly, which surprised her. “They are consumers. Neither good nor evil. They eat.”

“And why do they put things in those holes?”

He shook his head. “I am sure I have no idea,” he replied. “But I do know they devour pure mana. Their methods must have something to do with that.”

Zendikar: In the Teeth of Akoum (Magic: The Gathering), Chapter 8