When Officer Lopez arrives at the Lincoln's house he opens the door of the basement to search for Mrs. Lincoln. However in the previous scene were the family escapes through the window, the zombies clearly rip the basement door off the hinges when they enter.
When one of the characters is dead on the ground, his nostrils are continually flaring (because he is breathing).
The basement window they break out to escape has no window frame. It is just a piece of glass.
The part where the 2 people join Birdy in the basement, the man brings a heavy trunk to the top of the stairs as if to block the door from opening, but the door opened outwards from the basement. Unless he meant to trip a zombie, it wouldn't do anything to help keep the zombies out.