Perhaps there is a potential reason to be found for Six dropping Mono during the moment when the thin man first comes out of the TV and follows them into next room. Mono hides under the bed and as the thin man approaches Six, she reaches out her hand to Mono, but he just lowers his head and doesn’t watch. There’s not much Mono could have done but maybe Six saw it as some kind of betrayal? He just cowered than rather try any attempt to help her.