It's a nice sound, whatever it is. Beetle takes a look in the mud, a look at Kubo, and then promptly picks up the boy to place on his shoulders. No sandal? No problem.

"We'll get you another one," he promises, horned head swinging to look back towards Monkey. "May as well go see what it is, right?"

Don't mind him (and Kubo), just casually trying to find where the source is.