Scooby, who is ahead of Shaggy and Cass sniffing, comes nose to foot with one of the ghosts. When we pull back in the next shot, Cass and Shaggy are standing directly behind Scooby's tail. Wouldn't they have been able to see the monster before Scooby bumped into him?
While trying to find a door to escape the ghosts, Scooby runs past a revolving background plate with a door on it -- and he passes this door over and over again before reaching the door on the opposite side of the room.
The split in Cass's hair keeps moving from left to right throughout this episode.
Cass Elliot: If I ever get out of this I'm going on a strict diet of nothing but grapefruit, all for breakfast, lunch, dinner and in between snacks.
The alternate title to this episode is Scooby-Doo Meets Cass Elliot.
Cass Elliot died less than a year after this episode originally aired.