I loved discovering how the original Godzilla roar was made, in this article by Dawn Chmielewski on Re/code:
“It’s one of the most famous sound effects in cinema history,” said Aadahl. “We really wanted to embrace that and use the original as our template, and pay homage to that.”
The original film’s composer, Akira Ifukube, used a double bass, a leather glove and some pine tar to produce Godzilla’s trademark call.
“They’d rub the glove against the double base to create that groan,” Aadahl said.
The imagination of sound artists in those days blows my mind.