Where Did That Tooth Come From?

Overheard at our house about lunchtime...
Mom: "Okay, who is missing a tooth? I found one in the soap dish in your bathroom."
Blond Twin: "Sissy, open your mouth. Are you missing any teeth?"
Blond twin stares into the brunette twin's mouth counting missing teeth.
Blond Twin: "Nope. These are all the same teeth you were missing before."
Brunette Twin: "Open your mouth."
Brunette twin puts her finger in her sister's mouth and counts her missing teeth.
Brunette Twin: "Nope. You're not missing any new teeth either."
Overheard at our house at bedtime...
Blond Twin: "Daddy are you missing any teeth? We have one in the soapdish."
Daddy: "I found it on the carpet and put it there. It must belong to one of you."
Well, the mystery was partially solved. We know where the tooth came from, but don't know whose mouth originally came from.