When Stan says goodnight to Bigfoot, Bigfoot has white sclera instead of black.
When Stan goes into the bathroom to brush his teeth, Ollie is in the left bed. When Stan returns, Ollie is now in the right bed. Then, Stan has a close-up, and the shot returns to Ollie, who is now back in the left bed.
When Scooby hugs Stan, frightened, his left paw is flesh-colored.
The whole episode is an anachronism, as it is set in 1972, and Stan Laurel and Oliver Hardy were historical figures who died before that time. They are depicted as they looked sometime around 1932.
The "secret room" has windows, making it not so secret after all.