"Well now, I can only hope this is something of use to us."

For once he isn't trying to flirt or even flirting by proxy, he's just trying to see what he can do for his tet. And since Karkat has been singing for him for a while he might as well return the favor while he lets Karkat examine their gift.

The song he sings is slow and even, and in a language Karkat wouldn't recognize. It sounds calming, though, like a lullaby.