Admittedly, Madara Who Asks the Sage had been arrogant beyond measure.
But the White Snake Sage had seen plenty in her time. She exhaled a puff of smoke and declared in a tone that brooked no argument, "All who seek sagehood must pass the trial, then kowtow in greeting before I grant them sage power. Those are the rules, and there are no exceptions. Madara Uchiha, bow to me!"
What? She expected the great Madara Uchiha to kowtow to her?
Anger welled up in Madara, but after his experience in Shikkotsu Forest, he knew full well that the three great sages were reclusive monsters. Nothing good would come of falling out with them.
Before they came to Ryūchi Cave, Black Zetsu had said, "Lord Madara, as the saying goes, when you're under someone else's roof, you have to lower your head. Those old-timers just want people to flatter and revere them. Just humor them!"
Madara had scoffed. "Then I'll tear down the roof, and I can hold my head high!"
Such arrogance!
Still, arrogant though they both were, Madara had more maturity than Sasuke!
Rather than showing his anger, Madara asked calmly, "White Snake Sage, tell me, what does it mean to kowtow?"
The White Snake Sage answered without hesitation, "To strike the ground with your head is to kowtow!"
Madara asked again, "Then tell me, what is the ground?"
The White Snake Sage said, "The soil, bricks, and stones beneath your feet are the ground!"
"Very well..."
Crack! The corner of Madara's mouth lifted. He stamped his foot, and a brick beside it sprang into the air!
Madara caught the brick and smashed it against his forehead without so much as blinking!
Crunch!
The brick split apart, and blood streamed down his face!
"..." Even the White Snake Sage