I'm all about letting people's imaginations fill in the blanks. Problem is many people don't have the imagination to do so. The crew behind Netflix 'Bird Box' did us all a service by not showing the monster and the movie is that much better for it.
But if you absolutely gotta have it spelled out for you check the sfxatlas Instagram account below. And look! There's also a toy from Readful Things. If that's legit the real Bird Box Challenge will be trying to secure one of those before they sell out. Merchandising for a character that you never see... BRILLIANT!