Revealing mistake: When Ted Dansen gets buried in the sand, there isn't any extra sand piled up that was displaced by his body being in the hole.
Continuity mistake: Near the end of the "Father's Day" story, Sylvia gets impatient and goes to the kitchen calling to Mrs. Danvers. She sees the muddy footprints and investigates further. Mrs. Danvers' corpse falls against the back of the kitchen door with her face in the round window. As Sylvia lets go of the door, you can see the dead Mrs. Danvers blink as she slides across the window out of view.
Factual error: In the first story, Father's Day, it is dark at 7:00. In the middle of June, the sun stays up until at least 8. Or even 9 up north.