The Strangest Call of Carrion Crow I've Ever Heard. What Does “Kakong, Kakong…” Mean?

A carrion crow (Corvus corone, family Corvidae) perched in a defoliated tree of Japanese zelkova (Zelkova serrata, family Ulmaceae) in the backyard. This species usually calls in a raspy voice (“gaw” rather than “caw”). But this individual (sex unknown), who was one of a territorial pair in this neighbourhood, called repeatedly in a very strange voice, which sounded like “kakon, kakong ….” That wasn't an involuntary hiccup but a voluntary call. I wonder if its syrinx was damaged or malformed. Was it showing off the unique repertoire of vocalization? The carrion crow preened its black plumage between the unusual calls. Eventually, it hopped upward between leafless branches as if hiding from me. Captured candidly through a window pane and a lace curtain of my room in the cloudy early-afternoon (around 13:55 PM) of mid-March 2026 in Japan. It was a very exciting discovery/breakthrough for me because I’d had no idea who was emitting the mysterious call all year around. (I had even suspected a new species of frog or something!) For a full story (text in Japanese); https://sigma-nature-vlog.blogspot.com/2026/04/blog-post_03.html