What's the growl?

In my current pregnant state, I have taken up snoring. Not on purpose, but I have nonetheless. There are moments I wake myself up and realize that loud noise is actually coming from my mouth. Grace has noticed it, too. She and I will be snuggling on the couch in the morning and I must doze off because within a few minutes I hear her going, "Grrrroooaaarr." She thinks I am playing with her and growling in her ear so she growls back. Nice.