The Tooth Fairy doesn't work on Shabbos

When I picked LO up from school on Friday she eagerly showed me that she had lost a tooth. She was very excited because as I've reported before, the tooth fairy at our house pays BIG. However, with Shabbos here, there was no further mention of it and it totally slipped my mind.

On Shabbos morning when I went downstairs LO (with the saddest face in the world) said, "The tooth fairy didn't take my tooth." Having not had an ounce of coffee yet, I gave her all sorts of lame excuses, none that she seemed to buy, but she eventually just went back to her room. A little while later she came out and said, "I know why the tooth fairy didn't take my tooth! The tooth fairy doesn't work on Shabbos!" Geez...why didn't I think of that excuse?