MAN IS THE CREATURE HE FEARS

I really liked the whole idea/story around Bird Box. The threat of what's outside is far more than just that. If you look outside, you'll go insane and die. If you stay cooped up long enough with no answers as to what is going on, you'll also go insane. I love the dual threat from whatever is outside vs the threat of your neighbor.

Spoiler

Part of me believes there isn't a physical thing outside. The birds that Malorie and her housemates use to signal someone approaching the house reminds me of the birds used in mines to detect gas (an unseen, yet very harmful thing). I like to think the birds in the box are detecting some unseen force (which actually remains unseen, because no character can look at it and describe it for us).
I'm reminded of a line from Alfred Hitchcock's The Birds (1963) where Mitch (Rod Taylor) says something like "It's happening, isn't that reason enough?" In that film, there is no answer to why the birds do what they do, just like in Bird Box where there is no explanation as to what everyone is seeing outside.

Spoiler

Overall, this was a great read (and now I can finally watch the movie to compare). Highly recommend, it's a relatively quick read, as well!