"A twisted, demonic baby creature."
The whole point of the movie Bird Box is that nobody can look at the monsters which are the central premise of the movie. In a fate worse than the one suffered by those who meet medusa's gaze, anyone who looks at the Bird Box is driven to commit suicide. Luckily for us viewers of the film, the movie's director, Susanne Bier, decided to have the monsters remain unseen, which is likely why the blindfolds have already become so iconic.
Even though they weren't kept in the final cut, the monsters were actually made and the guy who sculpted them, Andy Bergholtz, has decided to show the world what could have been. According to him, the monster was originally going to be seen in a "'dream/nightmare sequence' with Sandra Bullock's character" and because of her "pregnant state and emotional arc thru the movie, the producers felt Sandra's nightmare would have something to do with a twisted, demonic baby creature attacking her." He also describes how this would only be the version of the monster that Bullock's character would see, owing to the fact that "the fatal 'vision' that each character saw would most likely be different for each person (you'll understand if you've seen the film)." Here are the photos, look at your own risk: