When the ape man is climbing the tree branch to get out of the pit that Alan had fallen into, he climbs with the commlock in his left hand, but when he reaches the ground above, the commlock is now in his right hand.
Near the end, when Helena backs into the mist, she and the other cavepeople emerge with their animal skins having magically transformed back into their moonbase uniforms.
When Koenig runs away from the yellow buggy, he lightly touches a giant boulder and it wobbles.
Since the Commander didn't know whether or not the landing party were, in fact, aboard Eagle Six (and since they only had a limited time that the moon would be within flying range of the planet), there wasn't a whole lot of logic in Koenig ordering the ship brought back to Alpha (removing the landing party's only form of sanctuary if they hadn't been on board). (Note: this plot device was necessary so Dr. Mathias could perform an autopsy on the caveman, which presented a key to the mystery).
The episode's epilogue lacked an explanation as to why the Alphans made no attempt to colonize the planet once their troubles had been resolved.
Within a few hours of the Alphans being cavemen, they managed to dig a large, perfectly square pit (that looked as though it had been done with a backhoe) without even the benefit of shovels.
At the episode's conclusion, Koenig stuns Alan, but Carter's back on his feet seconds later.
When the Spearman rips Sandra's shirt open, there's no sign of a bra. She was obviously wearing one during the previous scenes.
In one scene, as Alan Carter speeds away on the moon buggy, you can clearly see the chunks of dry ice on the ground used to simulate mist on the surface of the planet.