Fridge Horror: There is a lot of it in the movie: the ice cream man who appears to be eaten to shreds in the flick was far from the first person to be transported there and never to return to Earth, the lizard men who fell into the volcano were under mind control at the time and may have been good monsters, and so on. Just watch the flick.
The very first scenes of the movie feature a lost astronaut attempting to contact Mission Control just before he's eaten by Grumpy. Later in the movie Rick Marshall sees an empty spacesuit—but not the astronaut who was wearing it—in Grumpy's nest. How did Grumpy eat the astronaut and leave the suit behind???
He has a bizarre digestion system, from what we've seen. It's possible that he just processed the astronaut and not the suit.
Fridge Horror from the original series: If we do as many fans do, and just stick "The Circle" at the end of the second season as a nice tidy ending where both the Marshalls and Enik find their way home, then the only person left in the land with any understanding of the technology would be the Zarn. What might he do to the place (which would still have a few nice characters in it like Cha-Ka, Dopey, and S'Latch) if there's no one to stop him? For that matter, even if the Zarn doesn't make trouble, what will happen the next time a pylon breaks down if there's no one to fix it? Perhaps we can rest easy knowing that at least Holly will find her way back with a working knowledge of the pylons some day as Ranee.