Audio problem: When Markie is finally revealing to Helen who she is, Terry Burnham (Markie) is standing behind Janice Rule (Helen) talking to her over her shoulder and can be seen mouthing Janice's lines along with her in between her own.
A Passage for Trumpet - S1-E32
Audio problem: When Joey steps in front of the truck, a lady screams and it shows a close-up of her face. It pans out to a wider shot and for a moment, you can still hear the scream, but the woman's mouth is closed.
Answer: It's explained in the episode. The aliens are experimenting to see how humans react to various scenarios. This just happens to involve them using super strength.
Thanks. It's been a long time since I saw the episode so I forgot.