There was a reason why Yuber chose to hang around with monsters that didn't speak. However, every so often, there was an unfortunate exception, an exception that was troublesome to both parties.
The black knight could hardly fathom how the skeleton managed speech, but that was the least of his worries. Between wheezy gasps, the skeleton attempted to sing, "Happy biiiiiiirrssssday too youuuuuu!"
The fact that the skeleton finished the first line before Yuber diced and sliced it, made him wonder as to whether or not he was slacking.
Did Yuber hate singing or was his age getting to him?