My granddaughter was the first baby I ever knew who growled when content. When she did, you got the same feeling you get when the kid gets suspiciously quiet. I wrote Happy Growl when Kristin was about 6 months old. She learned to sing it at 3 and called it "Bubblegum." She did not remember growling, and the sound she made when singing the song was three-year-old imitating Grandma imitating rugrat.

Surprise, surprise, little brother Hans had the same quirk. A little different sound, but definitely a growl, and definitely a signal to go check out what he was up to.

Click to play Kristin's Happy Growl song.