I assumed it was a daytime, with the child minder thing and left it at that. Lo and behold, we're not home an hour before she's doing it for me too, complete with soaking wet, spit-soaked chin. I've heard tell of other children doing this, and I guess it's a developmental stage, but I just don't know what it means.
Will have to investigate further.
Update: Apparently, Emily blew razzies before at around 6 months and then stopped. We've surmised it might be something to do with teething still.