Ubum

I think that "Ubum" is how Penny says Mommy. I know it seems strange, but twice now I've tried to get her to say ma-ma-ma-ma and she responds by saying ma...ma...ubum..ubum. Today I said ma-ma to her and she looked at me and very intently said, "ubum." The only thing I can figure is that if you say the word "mommy" without the initial "m", as in "ommy" it can kind of come out like "ubum". It's a little wierd, but I'm pretty sure that's what she is doing.