Devil's Island

The Elvis tribute band was initially not supposed to be in the movie at all, but when attempting to get clearances to use the original recordings proved far more expensive than anyone had expected, a group of professional, Icelandic session musicians were hastily hired to provide the incidental numbers. So the "band" that features in the film is not comprised of actors but of real musicians, really performing.

When Baddi drives his car from the airport after staying at his mother in the USA, another person is seen in his car, though he apparently comes back alone.

References The Bad Seed (1956)