For the past couple of days, when villagers are supposed to be singing, they're just making a weird rapid noise while their eyes rapidly blink. It's either a bug or they're possessed.
Thanks, queentylerqueen. It worked. Eugene was freaking out and I put down the stereo and he instantly went into K.K. Calypso. I tried putting it down next to him when he wasn't singing and it didn't work, but I found out they can start dancing to the music, even changing how they dance as the songs change.
Edit: Alas, it didn't last. I took my stereo and when I came back, he was glitch singing again. Maybe I'll fix him and try saving.