Lately, whenever Z's content, I tell you, she fairly purrs like a cat, though not in the same way: it only sounds like it.
This is my first attempt. I thought I might try and catch her unawares making the sound, which you hear the slightest bit of in the very beginning; but upon review I realized it was kind of boring watching the back of her head, rocking like a champ, even if she were otherwise distracted by the camera.
Attempt number two: at the very start I'm trying to cue her to the purr because she's capable of repeating sounds now. And I'm gratified with a brief but unmistakable sample. At the end, Z manages to grab hold of the camera leash and yank it towards her for an unexpected close-up.