While Sanemi was with Shinobu Kocho at the butterfly mansion he saw one of the other demon slayers he’s seen but never actually spoke to them.

“Hey Kocho, What breathing do they use?”

Shinobu Kocho thought about it for a moment and spoke.

“Oh them? They use Sound and another one they made on their own you’re gonna have to ask for the second one though.”

“Okay I’ll ask later thanks Kocho.”

Sanemi replied and decided to go to the back to see who was training.