In
Tenchi Muyo,
Ryoko sometimes has a
tail. It looks like a
cat tail, and whether it's there or not doesn't seem to follow much of a
pattern.
This is one of the unexplained things in the Tenchi Muyo series. Other unexplained things are the technology of the planet Jurai, and how a cabbit weighing a few pounds can turn into a spaceship weighing many tons.