SPOILERS AHEAD IF YOU HAVEN'T SEEN THE MOVIE YET!
I think the most disappointing part of Bird Box for me was that you never see what's driving everybody crazy in the movie.
They get to safety and then bam, the movie ends. I was so angry! After all the stress I had been through on the river with Sandra, Boy and Girl on the river, I expected some answers.
Needless to say, the powers at be made the decision to pull the monster appearance before releasing the movie, but pictures have surfaced of what they were intended to look like. Pretty terrifying right?