When Foster drops his cases in the forest and goes back into the house, he never picks them up again.
During the breakfast scene, when the family is leaving the table, Frankie is holding a fork in front of him. Next shot looking over his shoulder, the fork is next to the plate and he picks the fork up.
There was absolutely nowhere near enough time for the dancers to get changed and made up before they did the Dance of the Dolls song.
After Ray Milland invites Frankie to a reading for the family, Frankie enters a room with the family waiting for him. Shortly afterwards, the daughter leaves the room and the shot shows her in the process of closing the door behind her. Frankie then leaves the room to go to her and the door is wide open.
During the breakfast scene (21 minutes in), Frankie takes the napkin ring off the napkin and places it on it's side, places the napkin on his lap, then reaches for the ring again and places it flat on the table so it won't roll away. Next in the alternate angle as the scene continues, the ring is on it's side again.
When Verity points a gun at Foster, it is a revolver with a silencer on; silencers don't work on revolvers. There is only one make of revolver that they can work on as the chamber moves to the barrel and this gun isn't it.
The smoke gun had plainly be heard squirting on the soundtrack when Foster is in the hall once Reggie has carried his daughter out.
When Frankie is in the snake house and a snake is at his face (around 1 hour 18 minutes in), a hand can be seen (on the left hand side of the screen) holding the snake. This is more visible on the Full Frame 4.3 as filmed version which is one of the special features on the U.K. DVD.
Between Foster going back into the house with Verity and going back out for the police, where did the fog suddenly come from?