Factual error: The scientists, having carefully charted their course to Earth, state that it is an 11 million mile trip from their planet. Not likely. Mars is our nearest planetary neighbor, and it's over 34 million miles away at its closest orbital approach. There are no planets any nearer to Earth than Mars. This is one of the very few cases where Rod Serling simply failed to do his astronomy homework.
Continuity mistake: No one drinks much lemonade, so there's neither time nor need for Eve to refill the pitcher during the brief cut to a scene on the porch. Yet after she has emptied its contents into the glasses on the tray, the lemonade pitcher refills itself.
Visible crew/equipment: Right after the phone conversation, everybody starts going towards the door. As they do, if you look at the couch on left you can very briefly see a shadow of something moving across it. It couldn't be any of the actors since they were all either outside or on the other side of couch.