* It ought to be pretty easy to eradicate the monsters if you can lure them anywhere by just making loud noises and they arrive one at a time, walk around slowly, completely blind, and can be taken down with just a single shotgun blast to the head.
* Where does the family get all of the electricity to run the lights and power the father's equipment, and if they have a generator for that, wouldn't the monsters have long since destroyed it?
* I know from experience that, if you're trying to stay quiet, you don't walk down the middle of a staircase, especially a rickety wooden one. A family like them would've long since learned to walk up and down the sides of the staircase, instead.
* A mother who's raised three kids ought to know that the way to quiet a baby is to put it against her heart, so that it can be soothed by her heartbeat. Instead, she holds the baby up above her collarbone, where its head has no contact with her body. It may be a minor thing, but it was an obvious one that took me out of the scene. Besides, imagine how much smarter the scene would've been if we'd seen the baby's head placed against her chest, heard a few beats of her heart and then heard the baby fall silent.
* The mother gets the sack caught on the nail and, even though she's supposed to be utterly quiet, she decides to pull even harder and use brute force to get past the hangup, rather than checking what it's caught on, so that she doesn't accidentally rip the bag and send the contents clattering down the steps.
* As silly as the placement and predictability of the nail was, it was distracting to see that it was still standing straight up in several scenes after that and the mother didn't seem to pay it any attention or even point it out to her kids so that they wouldn't step on it (and surely give them all away). Quickly showing her gently bending it back over, covering it with something or even just being sure that she and her kids didn't step anywhere near it would've addressed that.
* It was a little irritating that the monsters' weakness was revealed halfway through and it took the rest of the film for the daughter to figure it out (and, even at the end, she was really slow to realize). For the last half of the film, instead of wondering how they were possibly going to defeat/escape the monsters, I was just waiting for them to wise up and realize the ultimate solution that we already knew. Imagine if Signs had revealed halfway through that its monsters had a major weakness to water.
* On a related note, the poignancy of the father's sacrifice was muted for me because his daughter forced it (essentially, she got her own father killed) by turning off her hearing aid. If she had made the connection in the silo and left it on, the monster would've run off again and her father wouldn't have had to sacrifice himself for them. She's just a kid, but it irks me when writers can't think of any better way to explain a major moment like a character sacrificing himself than to have another character make a bad decision that we even know is one at the time.