8 Year old Girl with new spitting habit

My daughter just turned 8 and recently starting spitting randomly throughout the house whenever she feel like it; on the floors throughout the house (Hard floors or carpeted), in her room, in the kitchen sink (once with dishes in the sink), even on my bedroom floor. She does not hide to do this, but when confronted, she gets embarrassed.  When asked, why, she said she does not know.  Tonight, she spat on my bedroom floor and as a punishment,  I sent her to her room without any access to the television, or video games.  The only thing she was allowed to do is read a book.  She came back to my room 3 times, once to ask if I turned on the alarm (which she always seems to be concerned about) and the 2nd time while crying, to ask me if she can play her video games.  FYI: She never allows anyone to see her cry, ever since she was a baby…After the 2nd visit I told her she’s not allowed to leave her room until she can give me an explanation as to why she continues to spit on the floor.
After 10 minutes, she came back and told me that she remembered while playing on the playground the last week of school before summer vacation, a bug flew in her mouth and since then she always feels as though she has a bug in her mouth which give her the urge to spit.  So then I asked her, why not in the restroom, she claims, she is lazy.  I don’t believe lazy is the cause, because, once I found saliva on the floor, in the restroom, next to the toilet after she finished using the restroom...PLEASE HELP!