Wendy likes to sing when she carries her green snake around the apartment. "Singing" is the best way to describe her vocalizing; it's more operatic and sustained than meowing, and more varied and tuneful than howling. (Try singing with a fuzzy toy in your mouth and see how you do. It's not easy.)
She performs for a couple of minutes several times a week. We love hearing her, even when she wakes us in the night, because she sounds so happy and confident. When she does it while I'm on the phone with someone, the caller always hears her loud and clear.
We have no idea why she does this; our vet says it's a victory song, and she does sound proud. But it's not like that snake puts up more of a fight than her other toys; and she never sings with anything else. She's ignored the many other snakes I've gotten her after I noticed that old Green Snakey wasn't looking so chipper after years of being carried around in her mouth. And I never knew an outdoor cat to walk around singing while carrying a dead bird or mouse. Cats tend to keep that stuff on the QT so other cats won't try to take the victim for their own supper. The point is to eat it; not serenade it.
While none of my other cats has ever sung while carrying anything,* I know that plenty of cats do this sort of thing. It's hardly unique, but that doesn't make it any less baffling. I would love to know what's running through their minds... but then I would always love to know that.
But there's something else that baffles me, which other cat people can enlighten me about: do all cats sing in key and in rhythm when music is playing, as Wendy often does? She just sang along to a Traveling Wilburys tune, meowing on the beat and in the right key. She's harmonized with a few Springsteen songs, too, and meowed along to a few Christmas carols as well. Since cats aren't supposed to care for our music, that seems very weird, and it's happened too often to be a coincidence. Wendy is a near-total mystery to me for many reasons, but I do know that she likes Tom Petty and Bruce.
* I once had a cat who meowed along to certain Chopin and Brahms piano melodies, but he didn't have a toy in his mouth.