"We did not know — because we had not seen Black Panther because they were still making Black Panther — about their war chants," Joe Russo notes on the commentary. "And they just started doing it."

"Oh, my God, yeah," Anthony Russo interjects.

Both Marvel films were in production in Atlanta at the same time, which made it easier for castmembers to go back and forth between sets.

Calling the moment "incredibly cool," the brothers say fan favorite M'Baku actor Winston Duke took charge with the now classic chants, exactly as the leader of the Jabari tribe would in that situation.

"And after watching Winston doing it in the opening of the sequence, it led to the responding war cry that T'Challa (Chadwick Boseman) leads," Joe Russo says. "A year ahead of time, we had no idea 'Wakanda forever!' was going to be amazing."

Avengers: Infinity War is available digitally now and on Blu-ray on Aug. 14.