The creatures keep changing size. During one scene, the creatures aren't much bigger than a few inches, as they hide behind the books. But, when they go outside to cut the cables, they are as tall as the trash cans.
(At around 00:57:30) Mr. Farnum arrives at the house in his car. As he runs out of the car his hands are empty. He enters the house and meets Joan with a briefcase suddenly in his hand. As he starts up the staircase he sets the briefcase down on one of the lower stairs and runs up with his hands empty. When he enters Sally's bedroom the briefcase is again in his hand, and he lays it down on a trunk at the foot of the bed.
(at around 1h 5 mins) When the creatures cut the electric cable and plunge the house into darkness, when Joan is outside trying to get back into the house after looking at the fuse box, it's daylight out - or at least twilight. However, just a few moments earlier, when she was in the bedroom with Sally and looked out the window, it was very dark outside, clearly night time. At the same time that this action is happening, Alex is driving back to the house with Mr. Harris, and it's clearly night. But as Joan is circling the house to get in, you can see sunlight casting shadows on the house and on the ground behind her.
The dinner guests are told their names are written down indicating their places at the table. Yet, everyone seems to head directly to their assigned seat. If you've ever had to find your name at a seat you know this scenario is ridiculous.