Goofs

The basement window is hinged at the bottom and is open at the top into the room. Then, when Shaggy/Wilby goes through the window, it is hinged at the top and opens outward on the bottom.

Right after Franceska cleans the cut above Buzz Miller's eye, the cut disappears.

Francesca says that Lucretia Borgia lived during the "Dark Ages"; she actually died in the early 16th century, during the Renaissance.

In the scene where the boys launch the missile interceptor, the dining room's furnishings (the vase and cabinet behind Fred MacMurray) start to shake before the rocket can be heard to be ignited.

At the beginning, when Wilson Daniels and his wife lean in and kiss each other at the breakfast table, their lips clearly don't touch each other at all.

The inscription in the ring reads "In canis corpore transmuto", which is supposed to mean "I transmute into a dog's body" in Latin. That is, however, a grammatical mistake, because the correct Latin sentence should read "... in canis corpus..." (in the accusative case) instead of "... in canis corpore..." (which is the ablative case).

Wilby (in dog form) makes a phone call from a pay phone, but has no pockets in which to have a dime to make the call.

When Thum comes to visit Dr. Andrassy at his home, Dr. Andrassy seems a little surprised and tells him, "I told you never to come here at night." At the end of the scene, Dr. Andrassy says to Thum that he'll seem him at the doctor's home again the following night at 8:00pm, even though at the beginning of the scene he told him never to go to his house at night.